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Background and Objectives: Plant growth-promoting rhizobacteria (PGPR) with a diverse set of traits can improve crop yield in agriculture. The current study aimed to evaluate the potential of multi-trait PGPR isolates as inoculants for maize (Zea mays L.) growth. Materials and Methods: In this study, 23 bacterial isolates were initially screened from maize plant rhizosphere. Ten isolates (A1-A10) were selected based on N fixation, P and K solubilization and their in vitro specific PGPR traits, such as solubilization of Zn, and Mn, the production of IAA, siderophore, ammonia, and HCN were assayed. Finally, the potential of selected isolates in enhancing the germination, height, shoot collar diameter, shoot fresh and dry weight biomass, and root dry weight of maize were evaluated. Results: Among the positive-PGPR colonies, the selected isolates demonstrated the better performance of PGPR traits such as highest nitrogen fixation, P, K, Mn, and Zn solubilization, and production of siderophore, HCN, NH3, and IAA. In addition, the maize seed germination and improvement of maize yield in a pot experiment were observed after their treatment by bacterial inoculants. Biochemical characteristics, 16S rDNA amplification, and sequencing demonstrated a high similarity of PGPR isolates to the strains of Enterobacter, Pantoea, Kluyvera, Lelliottia, Klebsiella, Pectobacterium, and Stenotrophomonas. Conclusion: The findings demonstrated that these strains could prove effective PGPR inoculants for the improvement of maize crops as multiple bio-fertilizers. [ABSTRACT FROM AUTHOR]

Persistent crude oil contamination poses a significant environmental challenge. In this study, the efficacy of Vigna unguiculata (L.) and associated rhizospheric microorganisms in remediating crude oil-contaminated soil within a microcosm setting was investigated. A randomized block design was employed, and soil samples were subjected to varying degrees of contamination: 0% (UR), 2.5% (CR2), 5.0% (CR5), 7.5% (CR7), and 10.0% (CR10) w/w crude oil. The investigation aimed to assess the potential of Vigna unguiculata (L.) in mitigating crude oil contamination across these defined contamination gradients. The plant growth and crude oil removal were monitored concurrently post-emergence. Plant emergence and growth were significantly affected due to contamination, especially among plants in CR5 and CR10. The bacterial population was higher in the rhizosphere, and the treatments with lower hydrocarbon contamination. It was shown that plant density encouraged the growth of bacterial communities. Significant reduction in soil TPH was observed in CR2 (76.61%) and CR7 (65.88%). There was a strong correlation between plant growth and oil-utilizing bacterial population (r2 = 0.966) and plant growth and hydrocarbon reduction (r2 = 0.956), signifying the role of plant-bacterial synergy. Saturate fractions (C30 – C32) were significantly degraded to lower molecular weight compounds (C11 – C14). Except in CR5 and CR10, the remediation within the cowpea rhizosphere was effective even at regulatory standards. Understanding the rhizosphere ecological dynamics would further highlight the role the bacteria played; hence, it is recommended. NOVELTY STATEMENT: The present study established a direct link between bacterial-plant interaction and biodegradation of crude oil. It extensively explored the nature of the degradation and also the fate of the residual oil. The present study achieved high rate of TPH removal within 12 weeks using cowpea alone as against the several previous reports that used other stimulants. [ABSTRACT FROM AUTHOR]

Drought can seriously affect the yield and quality of tea. The interaction between rhizosphere microorganisms and tea plants could enhance the drought resistance of tea plants. However, there are few studies on the effects of abundant and rare microorganisms on tea plants. In this study, the contributions of abundant and rare bacteria in the rhizosphere microorganisms of 'FudingDabaicha' and 'Baiye No.1' to the resistance of tea plants to drought stress were studied using 16SrRNA sequencing, co-occurrence network analysis, and PLS-PM modeling analysis. By measuring the contents of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), malondialdehyde (MDA), proline, soluble sugar and soluble protein, it was found that the activity of antioxidant enzymes and the content of osmotic substances increased significantly after drought stress (p < 0.001). In the co-occurrence network of the two varieties, the average degree, clustering coefficient, and modularity index of the rare bacteria were greater than those of the abundant bacteria, and the path coefficient of the rare bacteria to drought was greater than that of the abundant bacteria. The contribution of rare microorganisms in 'FudingDabaicha' to drought stress was greater than that in 'Baiye No.1'. The rare bacteria of the two varieties were positively correlated with amino acids and negatively correlated with lipids. The results of this study will provide new insights for the use of rhizosphere microorganisms in improving the drought resistance of tea plants. [ABSTRACT FROM AUTHOR]

The phytoremediation efficiency of heavy metal‐contaminated saline soils is limited by low plant biomass and low accumulation of salt or heavy metals. Arbuscular mycorrhizal fungi (AMF) can directly promote plant growth or indirectly affect plant growth by regulating rhizosphere microbial communities; however, few studies have investigated the regulation of AMF on rhizosphere bacteria in heavy metal‐contaminated saline soils. This study investigated the effects of AMF (Funneliformis mosseae) on the growth and rhizosphere bacteria in Astragalus adsurgens Pall. and Stipa grandis P. Smirn. in cadmium (Cd)‐contaminated saline soils. The results revealed that F. mosseae improved the growth of the two grasses through distinct strategic mechanisms. In A. adsurgens, F. mosseae decreased shoot sodium ion (Na+) and Cd concentrations, increased Na+, Cd, and nutrient accumulations, enhanced the stability of the interaction network of the top 15 bacterial species with significant differences, and resulted in higher resistance of bacteria to external disturbances. F. mosseae increased the relative abundances of Paludibaculum, Pedomicrobium, and Aquicella, which positively correlated with biomass, Na+, and Cd accumulations. In S. grandis, F. mosseae promoted Na+, Cd, and nutrient accumulations and regulated interactions among the top 15 bacterial species with significant differences. Total nodes, total links, and average degree of the network increased, indicating a closer and more complex relationship between bacteria. F. mosseae increased the relative abundance of Devosia, Exiguobacterium, Pseudoxanthomonas, and Aliihoeflea, which positively correlated with biomass, Na+, and Cd accumulations. This study presented data to support plant‐mediated remediation of heavy metal‐contaminated saline soils using AMF symbiosis. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) is a potentially harmful metal with significant biological toxicity that adversely affects plant growth and physiological metabolism. Excessive Cd exposure in plants leads to stunted plant growth owing to its negative impact on physiological functions such as photosynthesis, nutrient uptake, and water balance. Potassium-enriched biochar (KBC) and Bacillus altitudinis rhizobacteria (RB) can effectively overcome this problem. Potassium-enriched biochar (KBC) significantly enhances plant growth by improving the soil structure, encouraging water retention, and enhancing microbial activity as a slow-release nutrient. Rhizobacteria promote plant growth by improving root ion transport and nutrient availability while promoting soil health and water conservation through RB production. This study examined the effects of combining RB + KBC as an amendment to rice, both with and without Cd stress. Four treatments (control, KBC, RB, and RB + KBC) were applied using a completely randomized design (CRD) in four replications. The results showed that the combination of RB + KBC increased rice plant height (38.40%), shoot length (53.90%), and root length (12.49%) above the control under Cd stress. Additionally, there were notable improvements in chlorophyll a (15.31%), chlorophyll b (25.01%), and total chlorophyll (19.37%) compared to the control under Cd stress, which also showed the potential of RB + KBC treatment. Moreover, increased N, P, and K concentrations in the roots and shoots confirmed that RB + KBC could improve rice plant growth under Cd stress. Consequently, these findings suggest that RB + KBC is an effective amendment to alleviate Cd stress in rice. Farmers should use RB + KBC to achieve better rice growth under cadmium stress. [ABSTRACT FROM AUTHOR]

Background: Citrus reticulata Blanco 'Orah' is one of the most widely grown citrus varieties in southern China. It has been proven that microbial and organic manure fertilization improve the yields and appearances of 'Orah' fruits. However, details regarding the mechanisms underlying the effects of combined fertilization on the agronomic traits and rhizosphere bacterial community of plants still need to be elucidated. Results: This study compared the rhizosphere bacterial community and carotenoids of 'Orah' with (WYT group) and without (WYCK group) combined fertilization in a local orchard in Wuming town from Nanning, Guangxi, China. The WYT group was sprayed with 50 ml Strongreen and 250 g of Yumeiren five times while WYCK group did not sprayed. Combined fertilization increased fruit weight and the Citrus color index (CCI) significantly (p < 0.05). By 16s rRNA sequencing, 7,126 operational taxonomic units (OTU) were obtained. A higher Shannon index was observed in the WYT group compared to that in the WYCK group. Comparison between the two groups showed that Pseudomonas was enriched in the WYT group with LDA (log10) score of 4.32, and Cyanobacteria was enriched in the WYCK group with LDA (log10) score of -4.11. At the family level, Phyllobacteriaceae (abundance mean: 0.0046 in WYCK vs. 0.0073 in WYT) was significantly abundant in the WYT group, whereas Thermosporothrix (abundance mean: 0.00053 in WYCK vs. 0.0019 in WYT) and Sphingobium (abundance mean: 0.00053 in WYCK vs. 0.0013 in WYT) were significantly abundant in the WYCK group. A total of 51 carotenoid components were tested by UPLC-MS/MS. In the pulp tissues, 37 carotenoid components were decreased in the WYT group compared to those in the WYCK group. In fruit skin, 24 significantly different components (7 downregulated and 17 upregulated) were identified in WYT compared to those in WYCK. Correlation analysis revealed that the network between OTUs and carotenoids contained seven carotenoid components and four OTUs. Four OTUs, strain TRA3-20 (a eubacterium), Roseiflexus, OPB35, and Fictibacillus correlated to carotenoid accumulation regulation in fruit skin. Conclusions: This study demonstrates the impact of the fertilization on soil microorganisms and carotenoid components. It constructs the regulatory network contained four OTUs for seven carotenoid components, providing evidence on precise fertilization in Orah. [ABSTRACT FROM AUTHOR]

Rhizosphere ecological factors that affect sugarcane ratoons are crucial components in the feedback mechanisms between the sugarcane plant and soil environment. However, systematic investigations on these dynamics are lacking. Therefore, this study investigated the relationship between sugarcane ratoon decline and rhizosphere ecological factors. In first-year sugarcane ratoons, ecological factors such as soil available potassium content, soil nitrogen fixation, and soil peroxidase activity were significantly positively correlated with sugarcane growth (P < 0.05) compared to that of third-year sugarcane ratoons. Significant intergroup disparities in the rhizosphere soil microbial community structure were observed based on different ratoon ages (P < 0.01), while highly significant intergroup differences in endophytic microbial community structure were observed based on a Jaccard distance analysis (P < 0.01). Generalised additive model analysis revealed a significant positive correlation (P < 0.05) between sugarcane growth properties and the alpha diversity of rhizosphere soil bacteria and endophytic bacteria but a predominantly negative correlation (P > 0.05) between the alpha diversity of endophytic fungi and key sugarcane growth indicators. The deterioration of mainly non-microbial ecological factors in rhizosphere soil (P < 0.05) with increasing ratoon age may represent a significant factor contributing to sugarcane ratoon decline. The fungal community significantly impacted soil enzyme activity, while the microbial community indirectly influenced sugarcane yield through its effect on soil enzyme activity. Therefore, endophytic fungi, particularly Ascomycota species, may play a crucial role in sugarcane diseases. [ABSTRACT FROM AUTHOR]

Phosphorus plays a crucial role in regulating many of the plant's metabolic activities by enhancing physiological functions and stimulating biological activities such as nodulation, nitrogen fixation, and nutrient uptake in the soil rhizosphere environment. Inoculants of phosphorus solubilizing bacteria serve as an eco-friendly alternative technology that positively influences both soil sustainability and plant growth. The majority of North Shewa highland areas are characterized by low available phosphorus, primarily acidic, and exhibit strong phosphorus absorption. The objective of this study was to isolate and identify phosphorus solubilizing bacteria from the rhizosphere of lentils and characterize their phosphate solubilizing activity. The cultural, biochemical, physiological microbial analysis was conducted in the microbiology laboratory, department of biology. Pikovskaya's medium was utilized for the isolation, screening, and maintenance of phosphate solubilizing bacteria. Phosphate Solubilizing Bacteria were isolated using tri-calcium phosphate as the sole source of phosphorus in indicator plates. Fifteen phosphate solubilizing bacteria were isolated from lentil rhizosphere soil samples, among which six were the most efficient phosphate solubilizers designated as PSBYE, PSBYR, PSBYM, PSBYL, PSBW, and PSBSW. All isolates notably solubilized tri-calcium phosphate compared to the uninoculated control. The highest phosphorous solubilization was observed from the isolate PSBYL, with a value of 10.61mg/50ml, followed by PSBW with a value of 9.08 mg/50ml. The decrease in pH value correlated with the levels of tri-phosphate solubilization in the PVK broth by the PSB isolates. The pH dropped to 4.64 from the initial pH of 7.2 when grown in the broth, which suggests that the production of organic acids is likely the primary mechanism for phosphate solubilization. [ABSTRACT FROM AUTHOR]

Beneficial rhizosphere microorganisms are widely employed to shield crops from underground pathogen infections. In this study, we challenge this conventional idea by employing rhizosphere soil bacteria to safeguard kiwi plants against the above-ground canker, caused by Pseudomonas syringae pv. actinidiae (Psa). Microbiome comparisons were conducted in different resistant cultivars Actinidia chinensis var. deliciosa 'Hayward' and A. chinensis var. chinensis 'Hongyang'. Our findings reveal the most notable disparity in the rhizosphere soil microbiome, with the Flavobacterium significantly enriched in the rhizosphere soil of more resistant cultivar, 'Hayward'. We isolated Flavobacterium isolates and observed their efficacy in preventing Psa infection, which is further confirmed in field trial by using a representative strain Flavobacterium soyae F55. Furthermore, undescribed gene clusters responsible for antimicrobial metabolite biosynthesis were identified in F. soyae F55, and F. soyae F55 growth was evidently promoted by the root exudates of 'Hayward'. The results underscore the potential of beneficial rhizosphere soil bacteria in protection against above-ground disease. A study highlights the potential of beneficial rhizosphere soil bacteria not only for controlling soil-borne diseases but also for providing cross-niche protection against above-ground diseases. [ABSTRACT FROM AUTHOR]

Introduction: There is a close and complex interaction between the elements in the aboveground-underground ecosystem during the growth and development of plants. Specifically, when the aboveground part of plants is infected by pathogens, it induces the plant rhizosphere to synthesize specific root exudates. Consequently, a group of beneficial rhizosphere soil bacteria is recruited to help plants resist diseases. However, the changes in the rhizosphere soil bacterial community of plants under infection by oomycete pathogens remain unknown. Methods: Three experimental treatments were set up in this experiment: soils inoculated with P. nicotianae , no-inoculation with P. nicotianae , and a control. The control treatment was composed of soils without transplanted tobacco plants, with the pathogen inoculated twice at an interval of eight days to ensure a successful P. nicotianae infection. P. nicotianae inoculation treatments were designed using the hyphal block inoculation method. In the non-inoculation treatment, tobacco plants were grown normally without pathogen inoculation. The tobacco plants were grown in a greenhouse. Results: This study demonstrates that tobacco plants recruit microorganisms at the rhizosphere level as a defense mechanism against disease after infection by the oomycete pathogen Phytophthora nicotianae. Specific rhizosphere soil bacteria were screened in vitro to promote tobacco growth in a biofilm-forming manner, which induced the systemic resistance of the plants to P. nicotianae. The recruitment of rhizosphere soil bacteria to the inter-root zone of tobacco plants after infection by P. nicotianae can help subsequently cultivated tobacco plants in the same soil resist pathogen infestation. Discussion: In conclusion, the present study confirms that infestation caused by oomycete pathogens alters the composition of the plant rhizosphere soil bacterial community and recruits a specific group of beneficial microorganisms that induce disease resistance and promote plant growth, thereby maximizing the protection of progeny grown in the same soil against the disease. [ABSTRACT FROM AUTHOR]

Background: The assembly of the rhizosphere community, even the diazotroph community, is mainly shaped by soil environmental factors (including soil climate and physiochemical characteristics) and plant selection. To better understand the driving forces on the active overall and nitrogen-fixing bacterial community compositions, we characterized the communities of tobacco rhizosphere soil collected from three sampling sites with a large geographic scale (> 600 km). Results: The results indicate that the diversity and community composition of the overall bacterial and diazotroph communities are obviously differed according to the sampling sites. Still, no significant difference is found between the communities in rootzone and rhizosphere samples. Climate variables including mean annual precipitation (MAP) and mean annual temperature (MAT), soil physiochemical characteristics including available nitrogen (AN), available potassium (AK) and pH are main factors that affect the bacterial and diazotroph community structures in the three sampling sites. Furthermore, MAP and MAT, AN and available phosphorus (AP), total nitrogen (TN) and organic carbon (OC), AK and electrical conductivity (EC) showed similar effects, but pH showed independent effect on the composition of the overall bacteria and diazotroph communities. However, the alpha diversity indices of active overall and nitrogen-fixing bacteria in the rhizosphere are obviously higher than in the rootzone samples, and no significant differences are observed among different sampling sites. Proteobacteria is the predominant active phylum of all samples for overall and nitrogen-fixing bacteria. Escherichia-Shigella, Achromobacter, Streptomyces and Sphingomonas are the dominant active bacterial genera, and Bradyrhizobium, Skermanella and Extensimonas are dominant active nitrogen-fixing bacteria genera in rhizosphere. Furthermore, the high active abundance of Escherichia-Shigella but low abundance of Ralstonia in all three sampling sites indicate high root-knot nematode infection and low wilt disease endemic risk. Conclusion: These results indicate that soil environmental factors contribute more to the tobacco rhizosphere bacterial community assemblage, but the rhizosphere contributes more to the diversity of active overall bacteria and nitrogen-fixing bacteria in the community. Our study provides novel knowledge for the assemble of rhizosphere bacterial and active bacteria communities across a large geographical scale. [ABSTRACT FROM AUTHOR]

Basal stem rot disease caused by Ganoderma boninense is a major problem for oil palm cultivation. The research was conducted to obtain biocontrol agents from rhizosphere of oil palm to control the disease as part of sustainable pest management in oil palm plantation. Rhizosphere bacteria were isolated from rhizospheres of healthy oil palm trees. Isolation of bacteria was done using serial dilution method. The isolated bacteria were then tested for its antifungal activity against G. boninense in vitro using dual culture assay. The ability of the bacteria to produce antifungal compound was also determined by culturing the bacteria on ISP2 liquid media. Once the bacterial cells were removed, the crude metabolites were then tested against G. boninense using agar well diffusion and toothpick colonization. The result showed that several isolates demonstrated strong antifungal activity against G. boninense. Some isolates were also able to degrade chitin and to solubilize phosphate. Furthermore, the crude metabolites produced by the rhizosphere bacteria demonstrated the ability to inhibit the growth of G. boninense in the agar diffusion method. Colonization of the G. boninense on toothpick following soaking in the crude metabolites was also inhibited. The isolated rhizosphere bacteria (BARK7 and BARK15 in which identified as Burkholderia sp.) showed promising ability to be developed as biocontrol agent for basal stem rot disease of oil palm. [ABSTRACT FROM AUTHOR]

Despite the development of adapted popcorn cultivars such as UENF WS01, strategies such as bacterial inoculation are being explored to enhance plant resilience to abiotic stress. This study investigates the impact of drought stress on popcorn cultivation. Specifically, the aim was to identify the benefits of Bacillus cereus interaction with the drought-tolerant hybrid UENF WS01 for its morphophysiology and growth by comparing inoculated and non-inoculated plants under water-stressed (WS) and well-watered (WW) conditions. This evaluation was conducted using a randomized complete block design in a factorial arrangement. For WS with inoculation samples, there were significant increases in relative chlorophyll content, maximum fluorescence intensity, and agronomic water use efficiency. Chlorophyll content increased by an average of 50.39% for WS samples, compared to a modest increase of 2.40% for WW samples. Both leaf and stem biomass also significantly increased for WS relative to WW conditions. Overall, B. cereus inoculation mitigated the impact of water stress, significantly enhancing the expression of physiological and morphological traits, even when paired with a drought-tolerant hybrid. [ABSTRACT FROM AUTHOR]

Given the challenges of slow growth and low survival rates in the early stages of Parashorea chinensis cultivation, identifying sustainable methods to enhance seedling performance is critical for successful reforestation and conservation efforts. This study aimed to address these by investigating the growth-promoting effects of phosphate-solubilizing bacteria (PSB). One-year-old seedlings of P. chinesis were inoculated with PSB strains isolated from the rhizosphere soil of Parashorea chinensis H. Wang plantations Y3, W5, H8, and a mixed strain (Mix), with inoculated seedling as a control (CK). The effects of inoculation on seedling growth, photosynthetic physiology, plant nutrient status, and physiological indicators were comprehensively evaluated. Results showed that PSB inoculation increased seedling height and basal diameter growth of P. chinensis, with an increase of 1.56 cm and 0.53 mm compared to CK, respectively, though the differences were not significant. The Mix treatment significantly improved photosynthesis, with increases in net photosynthetic rate (106.3%), transpiration rate (93.89%), and intercellular CO2 concentration (75.51%) compared to CK. Nutrient levels including total nitrogen, total phosphorus, and total potassium were significantly increased by 15.98%, 25.54%, and 32.12%, respectively, in the Mix treatments compared to CK. Moreover, stress resistance also improved, with higher proline content, soluble sugar, and soluble protein levels. Antioxidant enzyme activities (SOD, CAT, and POD) were increased by 9.83%, 23.66%, and 292.32%, respectively, while MDA content was significantly reduced by 69.01%. The mixed strain treatment also significantly increased acid phosphatase activity by 111.88%. In conclusion, PSB inoculation, particularly with the mixed strain, promoted growth and nutrient uptake photosynthetic efficiency and stress resistance in P. chinensis seedlings, offering a promising biotechnological solution for improving seedling performance. [ABSTRACT FROM AUTHOR]

The use of plant growth-promoting rhizobacteria presents a promising addition to conventional mineral fertilizer use and an alternative strategy for sustainable agricultural crop production. However, genotypic variations in the plant host may result in variability of the beneficial effects from these plant–microbe interactions. This study examined growth promotion effects of commercial vegetable crop cultivars of tomato, cucumber and broccoli following application with five rhizosphere bacteria. Biochemical assays revealed that the bacterial strains used possess several nutrient acquisition traits that benefit plants, including nitrogen fixation, phosphate solubilization, biofilm formation, and indole-3-acetic acid (IAA) production. However, different host cultivars displayed genotype-specific responses from the inoculations, resulting in significant (p < 0.05) plant growth promotion in some cultivars but insignificant (p > 0.05) or no growth promotion in others. Gene expression profiling in tomato cultivars revealed that these cultivar-specific phenotypes are reflected in differential expressions of defense and nutrient acquisition genes, suggesting that plants can be categorized into "microbe-friendly" cultivars (with little or no defense responses against beneficial microbes) and "microbe-hostile" cultivars (with strong defense responses). These results validate the notion that "microbe-friendly" (positive interaction with rhizosphere microbes) should be considered an important trait in breeding programs when developing new cultivars which could result in improved crop yields. [ABSTRACT FROM AUTHOR]

Pearl millet (Pennisetum glaucum (L.) R. Br.), a vital C4 Panicoid millet crop, predominantly thrives in rainfed regions subject to various abiotic stresses, notably drought and cold stress, limiting its growth potential and yield. As climate change exacerbates water scarcity, understanding methods to mitigate drought's adverse effects becomes crucial. However, particular bacteria flourishing in the rhizosphere, demonstrating resilience to drought and skilled at nurturing plant health, are recognized for their ability to enhance growth under various abiotic stresses. The current study demonstrated the varying effects of Pseudomonas putida MTCC5279 (RA) on mitigating drought stress under low-temperature field conditions for the pearl millet genotypes PRLT2/89–33 (drought-tolerant) and H77/833–2 (drought-resistant). Plants of both genotypes are grown till panicle emergence and subjected to drought stress at the start of January where temperature also drops in field conditions. The compound effect of drought with low temperature severely affects the inflorescence of both the genotypes but RA-inoculated PRLT2/89–33 plants have better performance than their respective control and drought plants as well compared to H77/833–2 genotypes. Abiotic stresses markedly influenced growth metrics, osmolyte buildup, MDA levels, and the capability to scavenge reactive oxygen species (ROS), all of which saw positive modulation following the application of RA in PRLT2/89–33. To our knowledge, this study represents the first comprehensive examination of P. putida-mediated plant growth enhancement in pearl millet under the combined effects of abiotic stresses. [ABSTRACT FROM AUTHOR]

We had assembled a synthetic bacterial community (SynComH) from the rhizosphere microbiota of Haloxylon ammodendron, which enhance drought tolerance in Arabidopsis thaliana under laboratory conditions. Here we assessed the efficacy of SynComH, alone or in combination with SynComS, a consortium of previously identified growth-promoting bacteria from Crocus sativus, in increasing maize plants' fitness under optimal and water-deficit conditions. We were also interested in unveiling the mechanisms by which the bacteria confer drought tolerance. We first performed detailed greenhouse experiments on maize plants that were artificially inoculated with SynComS, SynComH, and SynComH+S, and measured 22 different plant morphological, physiological, biochemical, and histological traits under optimal and water-deficit conditions. Data were analyzed by different univariate and multivariate statistical methods. Lastly, we tested the effects of the SynComs on maize in field in a split-plot experiment with two irrigation regimes as main plots and SynComs as subplots. Results from both greenhouse and field experiments showed that all three SynComs had growth-promoting properties and improved growth-related traits, but only SynComH and SynComH+S were effective in ameliorating the drought stress. SynComH substantially enhanced drought tolerance by increasing stomatal conductance, photosynthesis rate, and proline content, while decreasing transpiration rate, leading to up to 700% increase of water use efficiency. Morphological and histological investigations suggested that these positive effects are probably attributed to modulation of plant stomatal density and xylem structure by SynComH. Besides the significance for practical agronomic use, our results suggest unprecedented capabilities of non-pathogenic bacteria in modulation of plant stomatal density. [ABSTRACT FROM AUTHOR]

The inoculation of forest species with plant growth-promoting bacteria has grown and is increasingly sought to reduce the use of synthetic products. Thus, the objective was to evaluate the effect of the interaction between endophytic bacteria and synthetic indole butyric acid (IBA) on the initial development of Corymbia citriodora x Corymbia torelliana (CcCt) plants. The treatments were established by factorial (6 × 2) + 1, in which the mini-cuttings were inoculated with Pantoea vagans strains 7URP1-6 (B07) and 45URP4-1 (B45), Priestia megaterium (B11), Exiguobacterium sibiricum (B19), Bacillus sp. (B58) and a control treatment with the inoculation vehicle only, followed by immersion in 0 or 1,000 mg kg− 1 of synthetic IBA, plus an additional control not inoculated and treated with 2,000 mg kg− 1 of IBA. In relation to the cuttings treated only with 2,000 mg kg− 1 of IBA, cuttings inoculated with bacteria B07, B11, B19, and B58 had a similar survival rate, an increase of 29–36% in the percentage of rooting and of 27–34% in plant height, produced rooted cuttings with larger collar diameters and greater dry mass of roots and shoots, and a greater number of colony forming units of bacteria in the rhizosphere and in root and shoot tissues. The inoculation of mini-cuttings of CcCt with B07, B11, B19 and B58, followed by immersion in 1,000 mg kg− 1 of IBA improved the development of rooted cuttings relative to inoculated cuttings without IBA treatment, although it is not known if the effect is directly attributable to these bacterial strains. [ABSTRACT FROM AUTHOR]

Tunicate maize (Zea mays var. tunicata A. St. Hil) is a landrace that constitutes a fundamental aspect of the socio-cultural identity of Ixtenco, Tlaxcala (Mexico) and represents an exotic phenotype whose kernels are enclosed in leaflike glumes. Despite multiple studies conducted worldwide on plant growth-promoting-rhizobacteria (PGPR) in commercial maize varieties grown under monoculture systems, very little is known about bacteria inhabiting native maize landraces in agroecosystems, but for tunicate maize such knowledge is non-existent. This research described and profiled functional groups of culturable rhizobacteria from tunicate maize at two phenological stages (tasseling and maturity/senescence) in a polyculture system, highlighting potential PGPR for biotechnological purposes. Ninety-five rhizobacteria were isolated and molecularly identified, and their physiological activities such as plant growth promotion, production of exogenous lytic enzymes, and antagonism against fungal pathogens were determined. The culturable rhizobacterial community associated to tunicate maize comprised 42 genera, dominated by Bacillaceae, Comamonadaceae, Microbacteriaceae, Micrococcaceae, Oxalobacteraceae, Pseudomonadaceae, and Rhizobaceae families. At tasseling stage, the identified bacteria corresponded to Arthrobacter, Priestia, Herbaspirillum, Pseudomonas, and Rhizobium, and exhibited redundant capabilities for stimulating plant growth and nutrition, and inhibiting fungal phytopathogens. At maturity/senescence stage, the main genera Arthrobacter and Microbacterium displayed lytic capabilities to support mineralization process. We recorded potential novel rhizosphere functional bacteria such as Rhizobium, Sphingobium, and Arthrobacter which are not previously described associated to maize landraces, as well as their bioprospection as PGPR detected at plant phenological stages poorly explored (like maturity/senescence). This taxonomic and functional diversity was attributed to the application of agricultural practices as well as the rhizosphere effect during specific phenological stages. Results described the diversity and functionality of culturable rhizosphere bacteria from tunicate maize in polyculture systems that allowed us the detection of potential rhizobacteria for further developing of biofertilizers and biocontrollers directed as biotechnology for sustainable agriculture, and for generating strategies for conservation of native plants and their microbial genetic resources. [ABSTRACT FROM AUTHOR]

Introduction: The rhizosphere is the zone of soil surrounding plant roots that is directly influenced by root exudates released by the plant, which select soil microorganisms. The resulting rhizosphere microbiota plays a key role in plant health and development by enhancing its nutrition or immune response and protecting it from biotic or abiotic stresses. In particular, plant growth-promoting rhizobacteria (PGPR) are beneficial members of this microbiota that represent a great hope for agroecology, since they could be used as bioinoculants for sustainable crop production. Therefore, it is necessary to decipher the molecular dialog between roots and PGPR in order to promote the establishment of bioinoculants in the rhizosphere, which is required for their beneficial functions. Methods: Here, the ability of root exudates from rapeseed (Brassica napus), pea (Pisum sativum), and ryegrass (Lolium perenne) to attract and feed three PGPR (Bacillus subtilis, Pseudomonas fluorescens, and Azospirillum brasilense) was measured and compared, as these responses are directly involved in the establishment of the rhizosphere microbiota. Results: Our results showed that root exudates differentially attracted and fed the three PGPR. For all beneficial bacteria, rapeseed exudates were the most attractive and induced the fastest growth, while pea exudates allowed the highest biomass production. The performance of ryegrass exudates was generally lower, and variable responses were observed between bacteria. In addition, P. fluorescens and A. brasilense appeared to respond more efficiently to root exudates than B. subtilis. Finally, we proposed to evaluate the compatibility of each plant–PGPR couple by assigning them a “love match” score, which reflects the ability of root exudates to enhance bacterial rhizocompetence. Discussion: Taken together, our results provide new insights into the specific selection of PGPR by the plant through their root exudates and may help to select the most effective exudates to promote bioinoculant establishment in the rhizosphere. [ABSTRACT FROM AUTHOR]

The mulch film (MF) management model of the agricultural field affects the physical and chemical properties of soil (PCPS) and the structure of the microorganism community; however, studies on the relationship between the rhizosphere microorganism community structure and the thickness of MF are still limited. To understand the interactions among the MF thickness, PCPS, and rhizosphere microorganism, a study was conducted by using an integrated metagenomic strategy, where tobacco rhizosphere soil was treated with four commonly representative and used thicknesses of MFs (0.004, 0.006, 0.008, and 0.010 mm) in Yunnan laterite. The results showed that agronomic traits such as the tobacco plant height (TPH), leaf number (LN), fresh leaf weight (FLW), and dry leaf weight (DLW) were significantly (p < 0.01) improved in the field mulched with the thickest film (0.010 mm) compared with the exposed field (CK), and there was a 6.81 and 5.54% increase in the FLW and TPH, separately. The correlation analyses revealed a significant positive correlation of the MF thickness with the soil water content (SWC), soil organic matter (SOM), total nitrogen (TN), available nitrogen (AN), total phosphorus (TP), and available phosphorus (AP; all p < 0.01), while the MF thickness was negatively correlated with the soil temperature (ST; p < 0.01). In addition, the community structure of the rhizosphere soil bacteria was significantly changed overall by the MF thickness, which also interfered with the function of the rhizosphere soil bacteria. The correlation analyses also showed that the abundance of Bradyrhizobium and Nitrospira was positively correlated with the MF thickness, while the abundance of Sphinsinomonas and Massilia was negatively correlated with it. This indicated that with the increase of the MF thickness, the ability of the rhizosphere soil to utilize N and remove harmful molecules was strengthened, while the capacity of the rhizosphere soil to degrade pollutants was greatly reduced. These findings provide additional insights into the potential risks of the application of different thicknesses of MFs, particularly concerning the PCPS and soil microbial communities. [ABSTRACT FROM AUTHOR]

Soil acidification represents a severe threat to tobacco cultivation regions in South China, exacerbating bacterial wilt caused by Ralstonia solanacearum. The comprehension of the underlying mechanisms that facilitate the restoration of rhizosphere microbial communities in “healthy soils” is imperative for ecologically managing tobacco bacterial wilt. This study focuses on acidified tobacco soils that have been subjected to continuous cultivation for 20 years. The experimental treatments included lime (L), biochar (B), and a combination of lime and biochar (L+B), in addition to a control group (CK). Utilizing rhizosphere biology and niche theory, we assessed disease suppression effects, changes in soil properties, and the co-evolution of the rhizosphere bacterial community. Each treatment significantly reduced tobacco bacterial wilt by 16.67% to 20.14% compared to the control group (CK) (p < 0.05) and increased yield by 7.86% to 27.46% (p < 0.05). The biochar treatment (B) proved to be the most effective, followed by the lime-biochar combination (L+B). The key factors controlling wilt were identified through random forest regression analysis as an increase in soil pH and exchangeable bases, along with a decrease in exchangeable acidity. However, lime treatment alone led to an increase in soil bulk density and a decrease in available nutrients, whereas both biochar and lime-biochar treatments significantly improved these parameters (p < 0.05). No significant correlation was found between the abundance of Ralstonia and wilt incidence. Nonetheless, all treatments significantly expanded the ecological niche breadth and average variation degree (AVD), enhanced positive interactions and cohesion within the community, and intensified negative interactions involving Ralstonia. This study suggests that optimizing community niches and enhancing pathogen antagonism are key mechanisms for mitigating tobacco wilt in acidified soils. It recommends using lime-biochar mixtures as soil amendments due to their potential ecological and economic benefits. This study offers valuable insights for disease control strategies and presents a novel perspective for research on Solanaceous crops. [ABSTRACT FROM AUTHOR]

AbstractA large number of beneficial microorganisms have been used as inoculants in agriculture to increase grain yield. The objective of the study was to evaluate the response of common bean (Phaseolus vulgaris) to inoculation and co-inoculation with rhizobia, azospirilla and cyanobacteria combined with doses of N-fertilizer. A field experiment was carried out in two growing seasons to assess twelve treatments using single and combined inoculation of rhizobia (Rhizobium tropici + R. freirei), Azospirillum brasilense, Anabaena cylindrica, and Calothrix brevissima, and application of 30 and 60 kg N kg ha−1 as topdressing in a factorial design. A control without N-mineral and inoculation was included. Co-inoculation of common bean (cv. IPR Curió) using A. cylindrica, C. brevissima with rhizobia, and A. brasilense, with the application of 30 kg N ha−1 in topdressing increases grain yields. Regardless of the growing season and the N dose, the dual inoculation of rhizobia and C. brevissima stood out in the increase of grain yield concerning the control without inoculation, showing that it is an efficient agronomic practice for common bean under tropical conditions. [ABSTRACT FROM AUTHOR]

The rhizosphere bacterium Pseudomonas protegens FD6, which is associated with the production of antibiotics such as pyoluteorin (PLT) and 2,4-diacetylphloroglucinol (2,4-DAPG), has strong antagonistic effects on phytopathogens. Hfq is a conserved RNA chaperone involved in the regulation of stress tolerance, antibiotic production, and bacterial virulence. Here, we determined the regulatory effects of Hfq on biocontrol traits in P. protegens FD6. Mutation of hfq in FD6 reduced the growth rate, swimming and swarming ability, and production of proteases, siderophores, and hydrogen cyanide (HCN). Transmission electron microscopy revealed that disruption of hfq led to the loss of flagella. Furthermore, Hfq exerted a suppressive effect on biofilm formation and PLT production while not affecting antagonistic activity and control effect against tomato bacterial wilt. However, Hfq positively regulated the production of 2,4-DAPG and activated the phlD expression. Additionally, mutation of hfq abolished the function of the type VI secretion system (T6SS) due to a decrease in the expression of T6SS-related genes. Overall, these results suggest that Hfq plays a pleiotropic role in modulating the expression of biocontrol trait-related genes in P. protegens FD6. [ABSTRACT FROM AUTHOR]

Background: Volatile organic compounds (VOCs) released by plants can act as signaling molecules mediating ecological interactions. Therefore, the study of VOCs mediated intra- and interspecific interactions with downstream plant physiological responses is critical to advance our understanding of mechanisms underlying information exchange in plants. Here, we investigated how plant-emitted VOCs affect the performance of an interspecific neighboring plant via induced shifts in root exudate chemistry with implications for root-associated microbiota recruitment. Results: First, we showed that VOCs emitted by potato-onion plants stimulate the growth of adjacent tomato plants. Then, we demonstrated that this positive effect on tomato biomass was attributed to shifts in the tomato rhizosphere microbiota. Specifically, we found potato-onion VOCs to indirectly affect the recruitment of specific bacteria (e.g., Pseudomonas and Bacillus spp.) in the tomato rhizosphere. Second, we identified and validated the compound dipropyl disulfide as the active molecule within the blend of potato-onion VOCs mediating this interspecific plant communication. Third, we showed that the effect on the tomato rhizosphere microbiota occurs via induced changes in root exudates of tomato plants caused by exposure to dipropyl disulfide. Last, Pseudomonas and Bacillus spp. bacteria enriched in the tomato rhizosphere were shown to have plant growth-promoting activities. Conclusions: Potato-onion VOCs—specifically dipropyl disulfide—can induce shifts in the root exudate of adjacent tomato plants, which results in the recruitment of plant-beneficial bacteria in the rhizosphere. Taken together, this study elucidated a new mechanism of interspecific plant interaction mediated by VOCs resulting in alterations in the rhizosphere microbiota with beneficial outcomes for plant performance. 4wKeniGUxY9GPejLMpvDe9 Video Abstract [ABSTRACT FROM AUTHOR]

The exchange of metabolites (i.e., metabolic interactions) between bacteria in the rhizosphere determines various plant- associated functions. Systematically understanding the metabolic interactions in the rhizosphere, as well as in other types of microbial communities, would open the door to the optimization of specific predefined functions of interest, and therefore to the harnessing of the functionality of various types of microbiomes. However, mechanistic knowledge regarding the gathering and interpretation of these interactions is limited. Here, we present a framework utilizing genomics and constraint- based modeling approaches, aiming to interpret the hierarchical trophic interactions in the soil environment. 243 genome scale metabolic models of bacteria associated with a specific disease-suppressive vs disease-conducive apple rhizospheres were drafted based on genome-resolved metagenomes, comprising an in silico native microbial community. Iteratively simulating microbial community members' growth in a metabolomics- based apple root-like environment produced novel data on potential trophic successions, used to form a network of communal trophic dependencies. Network- based analyses have characterized interactions associated with beneficial vs non- beneficial microbiome functioning, pinpointing specific compounds and microbial species as potential disease supporting and suppressing agents. This framework provides a means for capturing trophic interactions and formulating a range of testable hypotheses regarding the metabolic capabilities of microbial communities within their natural environment. Essentially, it can be applied to different environments and biological landscapes, elucidating the conditions for the targeted manipulation of various microbiomes, and the execution of countless predefined functions. [ABSTRACT FROM AUTHOR]

Bacillus species are among the most studied and commercially exploited biocontrol agents of plant‐parasitic nematodes. These antagonists may control nematodes by producing toxic or repellent substances, inducing systemic resistance in plants and disrupting nematode chemotaxis. Understanding the mechanism of action of antagonists increases the likelihood of success for microbiological nematicides under field conditions. Therefore, the objective of this work was to elucidate the mechanisms of action of Bacillus amyloliquefaciens strain BaNCT02 against Meloidogyne incognita. We assessed the potential of this strain for forming biofilm in roots and producing volatile and non‐volatile toxic substances. BaNCT02 did not induce systemic resistance in tomato plants against M. incognita. Scanning electron microscopy and chemotaxis analyses revealed that the bacteria form a biofilm on soybean roots and 67% of second‐stage juveniles of M. incognita are repelled by common bean roots treated with the antagonist. Additionally, BaNCT02 produces substances with toxic effects against eggs and juveniles of M. incognita, including volatile organic compounds such as 2‐undecanone and 2‐heptanone, as well as non‐volatile metabolites like proteases and chitinases. The suppressive effect of these substances on hatching and mortality of juveniles varied from approximately 70% to more than 90%. We concluded that B. amyloliquefaciens BaNCT02 forms a biofilm on root surfaces and produces volatile and non‐volatile metabolites with nematicidal and repellent effects against M. incognita. [ABSTRACT FROM AUTHOR]

Background: Microorganisms play pivotal roles in seagrass ecosystems by facilitating material and elemental cycling as well as energy flux. However, our understanding of how seasonal factors and seagrass presence influence the assembly of bacterial communities in seagrass bed sediments is limited. Employing high-throughput sequencing techniques, this study investigates and characterizes bacterial communities in the rhizosphere of eelgrass (Zostera marina) and the bulk sediments across different seasons. The research elucidates information on the significance of seasonal variations and seagrass presence in impacting the microbial communities associated with Zostera marina. Results: The results indicate that seasonal variations have a more significant impact on the bacterial community in seagrass bed sediments than the presence of seagrass. We observed that the assembly of bacterial communities in bulk sediments primarily occurs through stochastic processes. However, the presence of seagrass leading to a transition from stochastic to deterministic processes in bacterial community assembly. This shift further impacts the complexity and stability of the bacterial co-occurrence network. Through LEfSe analysis, different candidate biomarkers were identified in the bacterial communities of rhizosphere sediments in different seasons, indicating that seagrass may possess adaptive capabilities to the environment during different stages of growth and development. Conclusions: Seasonal variations play a significant role in shaping these communities, while seagrass presence influences the assembly processes and stability of the bacterial community. These insights will provide valuable information for the ecological conservation of seagrass beds. [ABSTRACT FROM AUTHOR]

Background: The root-associated microbiomes are crucial in promoting plant growth and development through symbiotic interactions with their hosts. Plants may shape their microbiomes by secreting specific root exudates. However, the potential mechanisms how plant species determine root exudates and drive microbiome assembly have been little studied. In this study, three wild tobaccos and one cultivated tobacco were used to investigate the commonalities and differences of both root-associated microbiomes and root exudates. Results: Amplicon sequencing results suggested that tobacco species significantly affected microbial communities in both the rhizosphere and root endosphere, with the strongest impact on the fungal community in the root endosphere. The microbial networks of wild tobacco species were more stable than that of the cultivated tobacco, and fungal members played a more important role in the networks of wild tobacco species, while bacterial members did so in the cultivated tobacco. The rhizosphere bacteria of wild tobacco species showed a higher functional diversity than that of the cultivated tobacco, while the bacteria in the root endosphere presented a contrary pattern. Metabolomics analysis showed significant differences in the composition and abundance of root exudates among the four tobacco species, and the greatest difference was found between the three wild species and the cultivated one. Correlation analysis showed the strongest correlation between metabolites and rhizosphere bacteria, in which O-benzoic acid (2-methoxybenzoic acid) had the most positive correlations with rhizosphere bacteria, while β-ureidoisobutenoic acid had the most negative correlations with rhizosphere bacteria. The rhizosphere bacteria Streptomyces, Hydrophilus and Roseobacter had the strongest positive correlations with metabolites, and the rhizosphere bacterium Nitrobacter had the most negative correlations with metabolites. Conclusion: This study revealed the differences of microbial communities and root exudates in the rhizosphere and root endosphere of four tobacco species, which can further improve our understanding of plant–microbiome interactions during crop domestication. [ABSTRACT FROM AUTHOR]

The distribution characteristics of the microbial community in rhizosphere soils of different altitudinal gradients were explored to uncover ecological factors affecting microbial community composition. In this study, the community variations of bacteria and fungi in the rhizosphere soil of Chrysanthemum indicum L. were analyzed. Samples were distributed along an altitudinal gradient of 300–1500 m above sea level in the Fuling watershed of the Three Gorges Reservoir area, China. The analysis was conducted using Illumina MiSeq high-throughput sequencing and bioinformatics analyses. Through correlation analysis with ecological factors, the altitude distribution pattern and driving factors of soil microbial diversity in the mountainous and hilly region of Chongqing were explored. According to the results, the richness and diversity of rhizosphere soil bacteria increased with altitude, while fungi were the richest and most diverse at an altitude of 900 m. The composition of the microbial community differed among different altitudes. Actinobacteria, Proteobacteria, Acidobacteriota, Chloroflexi, Bacteroidota, Ascomycota, unclassified_k_Fungi, Basidiomycota, and Mortierellomycota dominated the microbial community in rhizosphere soil. Correlation analysis showed that the distribution of rhizosphere soil microbial communities correlated with soil ecological factors at different altitudes. Moisture, pH, total nitrogen, total potassium, available potassium, urease, and catalase were significantly positively correlated with rhizosphere soil bacterial α-diversity, while their correlations with fungi were not significant. Variation partition analysis showed that the combined effects of soil physical and chemical factors, enzyme activity, and microbial quantity regulated bacterial community structure and composition. Their combined contributions (19.21%) were lower than the individual effects of soil physical and chemical factors (48.49%), enzyme activity (53.24%), and microbial quantity (60.38%). The effects of ecological factors on fungal communities differed: While the soil physical and chemical factors (44.43%) alone had a clear effect on fungal community structures, their combined contributions had no apparent effect. The results of this study not only contribute to a deeper understanding of the impact mechanism of altitude gradient on the diversity of rhizosphere soil microbial communities, but also provide a scientific basis for the protection and management of mountainous and hilly ecosystems. It lays a foundation for the future exploration of the relationship between microbial communities and plant–soil interactions. [ABSTRACT FROM AUTHOR]

Little information is available on how rhizosphere bacteria affect abscisic acid (ABA) levels in plants and whether these bacterial effects are associated with improved plant water status. In this study, we tested the hypothesis that the stimulation of plant growth may be associated with the ability of ABA to increase the hydraulic conductivity of roots through the up-regulation of aquaporin. To do this, we studied the effect of bacteria capable of producing ABA on a barley mutant deficient in this hormone. Measurements of hydraulic conductivity of the ABA-deficient barley mutant Az34 showed that its tissues exhibited a reduced ability to conduct water, which correlated with lower ABA content in plants. The inoculation of Bacillus subtilis IB-22 stimulated the growth of both the mutant and its parent variety. Also, under the influence of bacteria, the ABA content in plants increased, and the increase was more significant in the mutant. This effect was accompanied by an increase in hydraulic conductivity in the roots of the ABA-deficient mutant, and immunolocalization using antibodies against PIP2;1 and PIP2;2 aquaporins revealed an increase in their abundance. Thus, the results obtained support the hypothesis about the importance of a sufficiently high ABA content in plants to maintain the abundance of aquaporins, hydraulic conductivity and the growth of barley plants. [ABSTRACT FROM AUTHOR]

Bacillus species act as plant growth‐promoting rhizobacteria (PGPR) that can produce a large number of bioactive metabolites. Bacillaene, a linear polyketide/nonribosomal peptide produced by Bacillus strains, is synthesized by the trans‐acyltransferase polyketide synthetase. The complexity of the chemical structure, particularity of biosynthesis, potent bioactivity, and the important role of competition make Bacillus an ideal antibiotic weapon to resist other microbes and maintain the optimal rhizosphere environment. This review provides an updated view of the structural features, biological activity, biosynthetic regulators of biosynthetic pathways, and the important competitive role of bacillaene during Bacillus survival. [ABSTRACT FROM AUTHOR]

Plant growth-promoting rhizobacteria (PGPR) and seaweed extracts (SWE) individually improve crop performances, but the response of crops upon their combined use is less understood. A field experiment on maize was carried out to evaluate the effect of seed priming with PGPR and undiluted SWE on the growth, yield, and nutritional quality of maize and soil properties. A split-plot design comprising 15 treatment combinations was laid out with SWE as the main factor (no SWE, Kappaphycus alvarezii and Sargassum cinctum extract, and PGPR as sub-plot factor (no PGPR, Bacillus megaterium, B. subtilis, Paenibacillus polymyxa and Azotobacter chroococcum). The composition and properties of SWE and PGPR were assessed. Without SWE, seed priming with all PGPR enhanced cob yield, the maximum improvement (32%) over no PGPR being recorded with A. chroococcum treatment. However, SWE priming along with PGPRs had no additional yield advantage compared to PGPR used alone. In the presence of either SWEs, A. chroococcum treatment was superior to other PGPR for most of the crop parameters like yield, carbohydrates and micro-nutrients in grains. The higher nutrient uptake agreed well with soil nutrient status after harvest. There were no deleterious effects on any parameters due to co-priming with K. alvarezii or S. cinctum extract with A. chroococcum, which was not the case with B. subtilis treatment where there was a significant decrease in growth and yield parameters despite evidence of increasing bacterial colony count. The study suggests the need for assessing optimal SWE doses for combinatorial PGPR treatments. [ABSTRACT FROM AUTHOR]

It is unknown whether soil microbiota and soil bacteria isolated from the rhizosphere of selenium hyperaccumulator plants can affect selenium absorption by selenium non-hyperaccumulator plants. Here, we used pot experiments and split root experiments to investigate the role of soil microbiota and isolated rhizosphere bacteria from a selenium hyperaccumulator plant (Cardamine violifolia) in affecting selenium absorption by a selenium non-hyperaccumulator plant (Brassica napus), combining root metabolism analysis, microbiome profiling, strain isolation and its selenium absorption functional validation. We found that soil microbiota of Cardamine violifolia significantly increased the root selenium content by 31.8% and regulated root exudation by Brassica napus. Additionally, the application of upregulated long-chain organic acids + amino acids, long-chain organic acids + short-chain organic acids, ethanolamine, and 2-ketobutyric acid increased the selenium contents in the roots of Brassica napus by 69.6%, 38.4%, 81.2%, and 48.8%, respectively. Further investigation revealed that dominant bacteria were significantly enriched in the rhizosphere of C. violifolia compared to B. napus. After that, we isolated the rhizosphere bacteria of Cardamine violifolia and observed that Bacillus sp.-2, Chryseobacterium sp., and Pseudomonas sp., as well as their combined communities, significantly improved selenium absorption in Brassica napus. Moreover, the combined bacterial communities significantly regulated specific-root metabolism, enhanced rhizosphere soil available selenium content, promoted root development, increased expression levels of genes encoding selenium transporter in root. These findings provide insights into utilizing rhizosphere bacteria of selenium hyperaccumulator plants to increase selenium absorption by non-hyperaccumulator plants. [ABSTRACT FROM AUTHOR]

Plants have evolved various strategies for assembling rhizosphere microbiota in response to abiotic stressors. However, our understanding of rhizosphere bacterial community assembly and function under microgravity conditions is limited, especially when soil serves as the growth substrate. Here, using microgravity analogs, we compared the bacterial communities in both the rhizosphere and bulk soil of wheat plants grown in soil under normal gravity and simulated microgravity conditions through 16S rRNA gene amplicon sequencing. Our results revealed a decrease in rhizosphere bacterial diversity and an increase in the relative abundance of plant pathogens under simulated microgravity. Furthermore, simulated microgravity amplifies the contribution of deterministic processes in the assembly of rhizosphere bacterial communities and promotes functional redistribution of rhizosphere bacteria. To validate the roles of rhizosphere-enriched bacteria, we generated a synthetic microbial community (SynCom) of Methylorubrum extorquens NCIMB 9399 , Paracoccus marcusii MH1 , Massilia haematophila CCUG 38318 , and Brevibacillus nitrificans DA2 , four strains isolated from the rhizosphere under simulated microgravity conditions. The SynCom exhibited significant potential in promoting plant growth and enhancing plant defense. Our study not only provides insights into plant-rhizosphere microbial symbiosis under simulated microgravity conditions, but also lays the theoretical foundation for the development of soil-based space plant growth systems and engineered microbial communities. [Display omitted] • Simulated microgravity shifted the composition of rhizosphere bacterial communities of wheat. • Rhizosphere recruited beneficial bacteria for microbial equilibrium under simulated microgravity. • Simulated microgravity promoted the reallocation of potential ecological functions in rhizobacteria. • Beneficial rhizobacteria enhanced wheat growth and defense under simulated microgravity. [ABSTRACT FROM AUTHOR]

This study investigated the germination response to temperature of seeds of nine Arabidopsis thaliana ecotypes. They are characterized by a similar temperature dependency of seed germination, and 10 °C and 29 °C were found to be suboptimal low and high temperatures for all nine ecotypes, even though they originated from regions with diverse climates. We tested the potential of four PGPR strains from the genera Pseudomonas and Bacillus to stimulate seed germination in the two ecotypes under these suboptimal conditions. Biopriming of seeds with only the biofilm-forming strain Pseudomonas putida KT2440 significantly increased the germination of Cape Verde Islands (Cvi-0) seeds at 10 °C. However, biopriming did not significantly improve the germination of seeds of the widely utilized ecotype Columbia 0 (Col-0) at any of the two tested temperatures. To functionally investigate the role of KT2440's biofilm formation in the stimulation of seed germination, we used mutants with compromised biofilm-forming abilities. These bacterial mutants had a reduced ability to stimulate the germination of Cvi-0 seeds compared to wild-type KT2440, highlighting the importance of biofilm formation in promoting germination. These findings highlight the potential of PGPR-based biopriming for enhancing seed germination at low temperatures. [ABSTRACT FROM AUTHOR]

The microbial community plays a vital role in root–environment interactions, which affect plant performance under biotic stress. Rust disease significantly affects plant growth, which may also affect rhizosphere microbial community. However, there is a scarcity of studies investigating the microbial community of rhizosphere under rust disease stress. Iris lactea is a widely utilized plant in gardening and landscaping due to its versatility and ornamental value, but it is often susceptible to rust disease in landscape settings. In this study, we compared the bacterial communities between bulk soil (non-cultivated control), rhizosphere soil of healthy Iris lactea plants, and rhizosphere soil of Iris lactea plants infected with rust disease (rhizosphere-R). Results revealed significant alterations in the abundance and composition of bacterial communities associated with rust disease infection. Specifically, the rhizosphere-R samples exhibited a decreased Shannon index at 1.9% compared to bulk soil and the relative abundance of Proteobacteria was increased at 31.65%. Moreover, distinct changes in β-diversity were shown between bulk soil and rhizosphere samples. Notably, potentially pathogenic bacteria increased in abundance under rust disease stress, while beneficial bacterial taxa decreased. Overall, our results show that rust disease affects the rhizosphere microbial community, which emphasizes the ecological implications of plant–microbe interactions under biotic stress and implications for developing targeted rhizobacterial-based biocontrol strategies. [ABSTRACT FROM AUTHOR]

[Objective] This study screened rhizosphere-promoting bacteria with multiple growth-promoting functions from rhizosphere soil of Schisandra chinensis and explored the growth-promoting effects on S. chinensis seedlings to provide excellent bacterial resources for the development of microbial fertilizers. [Method] Cultivable bacteria were isolated and purified from rhizosphere soil of S. chinensis using the plate streaking method, and their abilities to fix nitrogen, deconvolve organic phosphorus, dissolve inorganic phosphorus and produce indole acetic acid, siderophore and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase were measured to screen strains with multiple growth-promoting functions.The screened strain was identified by constructing a phylogenetic tree based on 16S rRNA gene sequence, and its growth-promoting effect on S. chinensis seedlings was explored by pot experiment. [Result] A total of 85 bacteria were isolated from rhizosphere soil of S. chinensis.By measuring their abilities to fix nitrogen, deconvolve organic phosphorus, dissolve inorganic phosphorus and produce indole acetic acid, siderophore and ACC deaminase, strain 142 with strong comprehensive growth-promoting ability was identified.Its nitrogen fixation ability value was 1.56, organic phosphorus deconvolution ability value was 2.06, inorganic phosphorus dissolution ability value was 1.47, indole acetic acid mass concentration was 52.34 mg/L, siderophore expression amount was 49.65%, and ACC deaminase activity was 0.22.Strain 142 was identified as Serratia fonticola and pot experiment results showed that it could promote the growth of S. chinensis seedlings.After applying the strain, plant height was increased by 198.20%, stem thickness was increased by 53.05%, fresh weights of aboveground and belowground were increased by 92.95% and 73.95%, and dry weights of aboveground and belowground were increased by 111.76% and 98.33%, chlorophyll a and b content increased by 42.00% and 8.11%. [Conclusion] The screened growth-promoting bacterium S. fonticola 142 had evidently promoting effect on the growth of S. chinensis seedlings. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is crucial for tree growth and development, and it significantly influences the rhizosphere microbial community. However, the effects of phosphorus addition on the microbial communities in the rhizosphere soil of Idesia polycarpa remain understudied. In this study, two-year-old "Yuji" Idesia polycarpa seedlings were used to investigate the effects of phosphorus fertilization at four different levels of 0 g (control, CK), 0.92 g (low phosphorus, LP), 1.83 g (medium phosphorus, MP), and 2.75 g (high phosphorus, HP) per plant. The fertilizers were applied every 40 days over 120 days. MiSeq high-throughput sequencing of the 16S rRNA and ITS1 genes was employed to analyze the microbial community composition and diversity of bacteria and fungi in the rhizosphere soil under different phosphorus levels. The results showed that compared with CK treatment, the application of phosphorus fertilizer changed the physicochemical properties of the soil. The LP treatment significantly increased the soil pH, while the HP treatment group exhibited the highest soil-available phosphorus (AP) content. LP treatment significantly increased the number of microbial OTUs in the early and rapid growth stages and the richness and diversity of microbial communities. In addition, the bacterial community structure was significantly correlated with soil pH and AP, while the fungal community had no significant effect. The primary metabolic pathway function of bacteria in the rhizosphere soil of Idesia polycarpa seedlings is mainly metabolism, while fungi are mainly biosynthesis. Compared with CK treatment, 20 differential metabolic pathways were screened out in the bacterial community. Only two differential metabolic pathways were screened out in the fungal community by LP treatment at 120 days. In summary, applying low-level phosphate fertilizer is conducive to promoting the diversity of rhizosphere soil microorganisms. Therefore, potted planting of Idesia polycarpa seedlings is more suitable for applying low phosphorus levels. [ABSTRACT FROM AUTHOR]

The intensified concerns related to agrochemicals' ecological and health risks have encouraged the exploration of microbial agents as eco-friendly alternatives. Some members of Bacillus spp. are potential plant-growth-promoting agents and benefit numerous crop plants globally. This study aimed to explore the beneficial effects of two Bacillus strains (B. subtilis strain IS1 and B. amyloliquificiens strain IS6) capable of alleviating the growth of tomato plants against salinity stress and Fusarium wilt disease. These strains were able to significantly promote the growth of tomato plants and biomass accumulation in pot trials in the absence of any stress. Under salinity stress conditions (150 mM NaCl), B. subtilis strain IS1 demonstrated superior performance and significantly increased shoot length (45.74%), root length (101.39%), fresh biomass (62.17%), and dry biomass (49.69%) contents compared to control plants. Similarly, B. subtilis strain IS1 (63.7%) and B. amyloliquificiens strain IS6 (32.1%) effectively suppressed Fusarium wilt disease and significantly increased plant growth indices compared to the pathogen control. Furthermore, these strains increased the production of chlorophyll, carotenoid, and total phenolic contents. They significantly affected the activities of enzymes involved in antioxidant machinery and the phenylpropanoid pathway. Hence, this study effectively demonstrates that these Bacillus strains can effectively alleviate the growth of tomato plants under multiple stress conditions and can be used to develop bio-based formulations for use in the fields. [ABSTRACT FROM AUTHOR]

Male Idesia polycarpa, which display distinct morphological and physiological traits, exhibit greater adaptability to stressful environments than females. However, the connection between this adaptability and rhizosphere processes remains unclear. Here, we investigate the differences in root bacterial community structures between male and female plants at different developmental stages, identifying bacterial strains associated with plant sex through functional predictions. This study aims to inform the optimal allocation of male and female plants during cultivation and provide a theoretical basis for sex identification and breeding. Samples from seven-year-old male and female plants were collected during the flowering (May) and fruit ripening (October) stages. Rhizosphere nutrient content and bacterial diversity were analyzed using Illumina high-throughput sequencing technology. The results demonstrate that total nitrogen (TN), total carbon (TC), and available potassium (AK) varied between sexes at different times. No significant differences between male and female plants were observed in the Shannon, Simpson, and Chao1 indexes during the flowering period. However, the Chao1 and Shannon indexes were significantly higher at fruit maturity in male rather than female plants. The predominant phyla of rhizosphere bacteria were Pseudomonadota, Acidobacteriota, and Actinomycetes. Interestingly, from flowering to fruit ripening, the dominant phyla in both male and female plants shifted from Actinomycetes to Pseudomonadota. A significant correlation was observed between pH and AK and rhizosphere bacteria (p < 0.05), with metabolism being the main functional difference. This study provides preliminary insights into the functional predictions and analyses of bacteria associated with Idesia polycarpa. The above findings lay the groundwork for further investigation into the sex-specific differences in microbial flora across different developmental stages, elucidating the mechanisms underlying flora changes and offering theoretical support for the high-quality management of Idesia polycarpa. [ABSTRACT FROM AUTHOR]

Abstract Lead (Pb) is a stress that can cause problems with several aspects of a plant’s metabolism, potentially impeding the plant’s ability to grow and develop. The use of gibberellic acid (GA3), quantum dot biochar (QDBC), and rhizobacteria (RB) can be effective methods to overcome this problem. Gibberellic acid is a crucial plant hormone that regulates plant growth, cell division, tissue differentiation, flowering, photosynthesis, and transpiration rate. It also significantly impacts crop resilience to stress, affecting plant morphology, enzymatic activity, and physiology. Biochar, a soil supplement, enhances plant development soil health, and reduces stress effects. Due to its large surface area and porosity, it increases soil water-holding capacity, nutrient retention, and microbial activity. Quantum dots, semiconductor nanoparticles, have been proposed as a potential method to alleviate plant stress by acting as antioxidants, reducing oxidative stress, and controlling nutrient and growth regulators. Rhizobacteria, soil bacteria in plant roots, stimulate plant growth, nutrient absorption, and harvesting capacity. They produce phytohormones, increase mineral and nitrogen accessibility, and can induce systemic resistance (ISR), affecting plant defense. This study investigates the effects of combining GA3, QDBC, and RB as amendments to fenugreek, both with 500 Pb stress and without Pb stress. Treatments (control, 0.25 GA3mg/L-QDBC, 0.5 GA3mg/L-QDBC, 0.25 GA3mg/L-QDBC + RB, and 0.5 GA3mg/L-QDBC + RB) were applied in six replications using a completely randomized design. Results demonstrate that the combination of 0.5 GA3mg/L-QDBC + RB with 500 Pb stress led to significant enhancements in fenugreek shoot fresh weight (15.62%), root fresh weight (73.53%), shoot dry weight (24.00%), and root dry weight (36.53%) compared to the control. Additionally, there were notable improvements in chlorophyll a (57.23%), chlorophyll b (19.21%), and total chlorophyll (36.23%) compared to the control under Pb stress, also showing the potential of 0.5 GA3mg/L-QDBC + RB with 500 Pb stress. The study suggests that combining 0.5 GA3mg/L-QDBC + RB with 500 Pb stress can effectively mitigate Pb stress in fenugreek.

Abstract Cadmium (Cd) is a potentially harmful metal with significant biological toxicity that adversely affects plant growth and physiological metabolism. Excessive Cd exposure in plants leads to stunted plant growth owing to its negative impact on physiological functions such as photosynthesis, nutrient uptake, and water balance. Potassium-enriched biochar (KBC) and Bacillus altitudinis rhizobacteria (RB) can effectively overcome this problem. Potassium-enriched biochar (KBC) significantly enhances plant growth by improving the soil structure, encouraging water retention, and enhancing microbial activity as a slow-release nutrient. Rhizobacteria promote plant growth by improving root ion transport and nutrient availability while promoting soil health and water conservation through RB production. This study examined the effects of combining RB + KBC as an amendment to rice, both with and without Cd stress. Four treatments (control, KBC, RB, and RB + KBC) were applied using a completely randomized design (CRD) in four replications. The results showed that the combination of RB + KBC increased rice plant height (38.40%), shoot length (53.90%), and root length (12.49%) above the control under Cd stress. Additionally, there were notable improvements in chlorophyll a (15.31%), chlorophyll b (25.01%), and total chlorophyll (19.37%) compared to the control under Cd stress, which also showed the potential of RB + KBC treatment. Moreover, increased N, P, and K concentrations in the roots and shoots confirmed that RB + KBC could improve rice plant growth under Cd stress. Consequently, these findings suggest that RB + KBC is an effective amendment to alleviate Cd stress in rice. Farmers should use RB + KBC to achieve better rice growth under cadmium stress.

Abstract PGPR has a higher potential impact on agricultural crops. It enhances plant growth and development in a variety of adverse environmental conditions, including biotic and abiotic stresses. The PGPR is commercially vital since it is more efficient, safe for the environment, and beneficial to the economy. Nowadays, salt stress has an impact on the agricultural ecosystem. Salt-tolerant PGPR can directly stimulate plant growth and development by producing a variety of metabolites and phytohormones. The current study looked at the isolation of salt-tolerant bacterial species and their ability to stimulate plant development. Four bacterial species were chosen for their better salt stress tolerance (0–5%). They were identified by 16S rRNA sequencing: Solibacillus silvestris BR1, Peribacillus frigoritolerans BR2, Paenibacillus taichungensis CR1, and Solibacillus isronensis CR2. These strains were positive production of indole acetic acid with varying incubation periods (19.66 ± 1.528 to 646.111 ± 8.058 µg/mL), salt stress (ranging from 29.556 ± 1.171 to 147.8111 ± 2.086 µg/mL), phosphate solubilization (0.145 ± 0.011 to 0.921 ± 0.007 µg/mL), ammonium production (0.299 ± 0.047 to 1.202 ± 0.142 µg/mL), HCN production (0.308 ± 0.051 to 4.269 ± 0.069 µg/mL), and siderophore production (0.190 ± 0.064 to 1.543 ± 0.108 µg/mL) for control strains were used without salt stress. The production level was expressed using a standard curve containing various standards.

Abstract Background Soil bacteria often form close associations with their host plants, particularly within the root compartment, playing a significant role in plant growth and stress resilience. Vachellia tortilis subsp. raddiana, (V. tortilis subsp. raddiana)a leguminous tree, naturally thrives in the harsh, arid climate of the Guelmim region in southern Morocco. This study aims to explore the diversity and potential plant growth-promoting (PGP) activities of bacteria associated with this tree. Results A total of 152 bacterial isolates were obtained from the rhizosphere of V. tortilis subsp. raddiana. Rep-PCR fingerprinting revealed 25 distinct genomic groups, leading to the selection of 84 representative strains for further molecular identification via 16 S rRNA gene sequencing. Seventeen genera were identified, with Bacillus and Pseudomonas being predominant. Bacillus strains demonstrated significant tolerance to water stress (up to 30% PEG), while Pseudomonas strains showed high salinity tolerance (up to 14% NaCl). In vitro studies indicated variability in PGP activities among the strains, including mineral solubilization, biological nitrogen fixation, ACC deaminase activity, and production of auxin, siderophores, ammonia, lytic enzymes, and HCN. Three elite strains were selected for greenhouse inoculation trials with V. tortilis subsp. raddiana. Strain LMR725 notably enhanced various plant growth parameters compared to uninoculated control plants. Conclusions The findings underscore the potential of Bacillus and Pseudomonas strains as biofertilizers, with strain LMR725 showing particular promise in enhancing the growth of V. tortilis subsp. raddiana. This strain emerges as a strong candidate for biofertilizer formulation aimed at improving plant growth and resilience in arid environments.

Study of the mineralogical composition of soils in coal dumps formed in sectors of the Kemerovo region for further remediation of posttechnogenic landscapes.Samples of technogenically disturbed soils of the Mokhov, Korchakol and Barzas dumps located on the territory of the Kemerovo region were studied. The results were obtained using X‐ray diffraction analysis.The chemical composition of the soils of the Mokhovsky, Barzassky and Korchakolsky coal dumps have been determined. Chromium pyrophosphate (Cr2O7Р2), aluminium sulfphide (Al2S3) and zirconium silicide (ZrSi) prevail in the samples of the Mokhov dump, while the Barzas dump contains a significant amount of carbon (C), strontium zirconate (SrZrO3) and calcium carbonate (CaCO3).Based on these results, conclusions were drawn about the structure and some physical and chemical parameters of the soil.

Abstract Arsenic (As) contamination is a major environmental pollutant that adversely affects plant physiological processes and can hinder nutrients and water availability. Such conditions ultimately resulted in stunted growth, low yield, and poor plant health. Using rhizobacteria and composted biochar (ECB) can effectively overcome this problem. Rhizobacteria have the potential to enhance plant growth by promoting nutrient uptake, producing growth hormones, and suppressing diseases. Composted biochar can enhance plant growth by improving aeration, water retention, and nutrient cycling. Its porous structure supports beneficial microorganisms, increasing nutrient uptake and resilience to stressors, ultimately boosting yields while sequestering carbon. Therefore, the current study was conducted to investigate the combined effect of previously isolated Bacillus faecalis (B. faecalis) and ECB as amendments on maize cultivated under different As levels (0, 300, 600 mg As/kg soil). Four treatments (control, 0.5% composted biochar (0.5ECB), B. faecalis, and 0.5ECB + B. faecalis) were applied in four replications following a completely randomized design. Results showed that the 0.5ECB + B. faecalis treatment led to a significant rise in maize plant height (~ 99%), shoot length (~ 55%), root length (~ 82%), shoot fresh (~ 87%), and shoot dry weight (~ 96%), root fresh (~ 97%), and dry weight (~ 91%) over the control under 600As stress. There was a notable increase in maize chlorophyll a (~ 99%), chlorophyll b (~ 81%), total chlorophyll (~ 94%), and shoot N, P, and K concentration compared to control under As stress, also showing the potential of 0.5ECB + B. faecalis treatment. Consequently, the findings suggest that applying 0.5ECB + B. faecalis is a strategy for alleviating As stress in maize plants.

Seed priming enhances germination and growth, which are important determinants of crop yield. This study was carried out to assess the effect of priming duration and metabolite concentration on the priming of five (5) different crops, using the metabolites of five (5) bacterial isolates. The crop seeds were treated in the cold-extracted metabolites of the five isolates at five (5) different priming durations (1, 2, 3, 4, and 5 h) and then in five metabolite concentrations (200, 400, 600, 800, and 1000 mg/L) of the five extracted metabolites at the optimal priming duration determined in the first experiment. Characterization of the cold-extracted metabolites was also carried out using gas-chromatography-mass spectrometry (GC-MS). Results revealed that priming cowpea and soybean for longer durations (< 3 h) could hinder their growth and development. Lower concentrations were observed to be optimal for cowpea and soybean, but for sesame and okra, there was no detectable pattern with metabolite concentration. The GC-MS revealed the presence of some molecules (e.g. hexadecanoic acid) that have shown plant growth promotion potential in other studies. This study showed that seeds with large endosperm, such as, cowpea and soybean, are more prone to the deleterious effects of treatment for longer durations. Further experiments should be carried out to isolate and purify the bioactive moieties for further studies and onward application.

Plants can recruit beneficial microbes to enhance their ability to resist disease. It is well established that selenium is beneficial in plant growth, but its role in mediating microbial disease resistance remains poorly understood. Here, we investigated the correlation between selenium, oilseed rape rhizosphere microbes, and Sclerotinia sclerotiorum. Soil application of 0.5 and 1.0 mg kg–1 selenium [selenate Na2SeO4, Se(VI) or selenite Na2SeO3, Se(IV)] significantly increased the resistance of oilseed rape to Sclerotinia sclerotiorum compared with no selenium application, with a disease inhibition rate higher than 20% in Se(VI)0.5, Se(IV)0.5 and Se(IV)1.0 mg kg–1 treatments. The disease resistance of oilseed rape was related to the presence of rhizosphere microorganisms and beneficial bacteria isolated from the rhizosphere inhibited Sclerotinia stem rot. Burkholderia cepacia and the synthetic community consisting of Bacillus altitudinis , Bacillus megaterium , Bacillus cereus , Bacillus subtilis , Bacillus velezensis , Burkholderia cepacia , and Flavobacterium anhui enhanced plant disease resistance through transcriptional regulation and activation of plant-induced systemic resistance. In addition, inoculation of isolated bacteria optimized the bacterial community structure of leaves and enriched beneficial microorganisms such as Bacillus , Pseudomonas , and Sphingomonas. Bacillus isolated from the leaves were sprayed on detached leaves, and it also performed a significant inhibition effect on Sclerotinia sclerotiorum. Overall, our results indicate that selenium improves plant rhizosphere microorganisms and increase resistance to Sclerotinia sclerotiorum in oilseed rape. [ABSTRACT FROM AUTHOR]