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BackgroundMercury (Hg) is highly toxic and has the potential to cause severe health problems for humans and foraging animals when transported into edible plant parts. Soil rhizobia that form symbiosis with legumes may possess mechanisms to prevent heavy metal translocation from roots to shoots in plants by exporting metals from nodules or compartmentalizing metal ions inside nodules. Horizontal gene transfer has potential to confer immediate de novo adaptations to stress. We used comparative genomics of high quality de novo assemblies to identify structural differences in the genomes of nitrogen-fixing rhizobia that were isolated from a mercury (Hg) mine site that show high variation in their tolerance to Hg.ResultsOur analyses identified multiple structurally conserved merA homologs in the genomes of Sinorhizobium medicae and Rhizobium leguminosarum but only the strains that possessed a Mer operon exhibited 10-fold increased tolerance to Hg. RNAseq analysis revealed nearly all genes in the Mer operon were significantly up-regulated in response to Hg stress in free-living conditions and in nodules. In both free-living and nodule environments, we found the Hg-tolerant strains with a Mer operon exhibited the fewest number of differentially expressed genes (DEGs) in the genome, indicating a rapid and efficient detoxification of Hg from the cells that reduced general stress responses to the Hg-treatment. Expression changes in S. medicae while in bacteroids showed that both rhizobia strain and host-plant tolerance affected the number of DEGs. Aside from Mer operon genes, nif genes which are involved in nitrogenase activity in S. medicae showed significant up-regulation in the most Hg-tolerant strain while inside the most Hg-accumulating host-plant. Transfer of a plasmid containing the Mer operon from the most tolerant strain to low-tolerant strains resulted in an immediate increase in Hg tolerance, indicating that the Mer operon is able to confer hyper tolerance to Hg.ConclusionsMer operons have not been previously reported in nitrogen-fixing rhizobia. This study demonstrates a pivotal role of the Mer operon in effective mercury detoxification and hypertolerance in nitrogen-fixing rhizobia. This finding has major implications not only for soil bioremediation, but also host plants growing in mercury contaminated soils.

Fertilization management of pigeon peas can increase soil quality and the N utilization by plants. Therefore, we evaluated the biological activity of soil cultivated with pigeon peas (Cajanus cajan (L) Millsp.) under different fertilization treatments. A randomized block design was used with three replicates and a 3×5 factorial arrangement (genotype×fertilization and inoculation management). At full flowering stage, the plants were collected and shoot dry matter was evaluated. Soil was sampled at 0-20 cm for various analysis viz. nodulation assessment; soil organic carbon; total nitrogen; carbon and nitrogen from microbial biomass; C/N ratio; β-glucosidase and urease enzymatic activity. Data were subjected to analysis of variance and Tukey’s test (P ≤ 0.05). A Pearson correlation matrix was constructed, and the similarity between treatments was evaluated using the Mahalanobis distance and grouping was done using the unweighted pair group method with arithmetic average (UPGMA). Both the experimental genotypes (BRS03 and BRS04) showed similar nodulation and shoot dry matter pattern with respect to fertilizer treatments. Furthermore, the microbial inoculation promoted a higher shoot dry matter content in all the genotypes. The application of mineral N and inoculation increased the total N content in the soil, favoring the mineralization of this nutrient. During the testing phase, the genotypes exhibited an increase in microbial carbon and microbial quotient levels, indicating an improvement in soil quality. The combination of fertilization and inoculation increased the enzymatic activity of β-glucosidase and urease. The correlation matrix showed a strong association between N total and C/N ratio. The formation of groups by UPGMA was observed as a function of inoculation, demonstrating its effect on soil biological variables. [ABSTRACT FROM AUTHOR]

The functional and structural features of microbial load in soil are influenced by the presence of insecticides. This study examined the impact of two organophosphorus insecticides, dimethoate and parathion on the microbial load of soil. The colony count of fungi, actinomycetes, bacteria, and nitrogen fixing bacteria was reduced after insecticides application at 7 and 14 days, but at 28 days the colony count began to increase. The growth of two white rot fungi including Pleurotus sajor-caju and Phanerochaete chrysosporium was affected by parathion, which was reflected by a decrease in colony radius to 1.85±0.05 and 0.75±0.06 cm, respectively, and by dimethoate, reflected by a decrease in colony radius to 3.33±0.12 and 1.85±0.05 cm, respectively at 40 mg/L compared to colony radius at control 7.90±0.12 and 7.50±0.06 cm, respectively. The applied low concentration (10 mg/L) encouraged P. sajor-caju and P. chrysosporium to remove up to 87.7% and 81.8% of dimethoate, respectively, and 69.20 and 68.30% of parathion, respectively compared with the decomposition at high dose (40 mg/L) at 28 days. The presence of insecticides induced the production of ligninolytic enzymes lignin peroxidase, laccase, and manganase peroxidase. [ABSTRACT FROM AUTHOR]

During nutrient scarcity, plants can adapt their developmental strategy to maximize their chance of survival. Such plasticity in development is underpinned by hormonal regulation, which mediates the relationship between environmental cues and developmental outputs. In legumes, endosymbiosis with nitrogen-fixing bacteria (rhizobia) is a key adaptation for supplying the plant with nitrogen in the form of ammonium. Rhizobia are housed in lateral root-derived organs termed nodules that maintain an environment conducive to Nitrogenase in these bacteria. Several phytohormones are important for regulating the formation of nodules, with both positive and negative roles proposed for gibberellin (GA). In this study, we determine the cellular location and function of bioactive GA during nodule organogenesis using a genetically encoded second-generation GA biosensor, GIBBERELLIN PERCEPTION SENSOR 2 in Medicago truncatula. We find endogenous bioactive GA accumulates locally at the site of nodule primordia, increasing dramatically in the cortical cell layers, persisting through cell divisions, and maintaining accumulation in the mature nodule meristem. We show, through misexpression of GA-catabolic enzymes that suppress GA accumulation, that GA acts as a positive regulator of nodule growth and development. Furthermore, increasing or decreasing GA through perturbation of biosynthesis gene expression can increase or decrease the size of nodules, respectively. This is unique from lateral root formation, a developmental program that shares common organogenesis regulators. We link GA to a wider gene regulatory program by showing that nodule-identity genes induce and sustain GA accumulation necessary for proper nodule formation. Gibberellin patterning is a key difference between nodule organogenesis and lateral root organogenesis. [ABSTRACT FROM AUTHOR]

Water shortage is the most critical abiotic stress and adversely impacts crop growth and productivity. Biofertilizers are an environmentally friendly method for sustainable agricultural development and improving plant water deficit tolerance. The effects of biological and chemical fertilizers on yield, yield components, and nutrient absorption of chickpea plants were studied in 2018 and 2019. The main plots were assigned to the irrigation levels [80% (I80) and 50% (I50)] and the subplot was assigned to 13 fertilizer combinations including free-living N-fixing bacteria (NB), potassium solubilizing bacteria (KB), phosphate solubilizing bacteria (PB), common chickpea nutrition program (F; NPK chemical fertilizer), and their combination. The results showed that shoot phosphorus content was increased by 80% when F + NPB (NPK chemical fertilizer and N + P biofertilizers) was applied at I80 compared with the control at I50. Furthermore, I80 and the application of PKB (P + K biofertilizers) and NPKB (N + P + K biofertilizers) obtained the highest shoot K and N concentrations, respectively. The NPKF + B-treated plants (N + P + K chemical fertilizer and N + P + K biofertilizers) demonstrated superior growth attributes such as plant height and the number of sub-branches at I80. The highest grain yield was obtained from the NPKF + B treatment at I80, which was 7.1-fold higher compared with the control at I50. In general, the combined application of biochemical fertilizers mitigated the adverse effect of water deficit and improved nutrient absorption and chickpea yield. The use of biochemical fertilizers can be efficient in reducing the consumption of chemical fertilizers and achieving sustainable agricultural goals. [ABSTRACT FROM AUTHOR]

Many plant species form symbiotic associations with nitrogen-fixing bacteria. Through this symbiosis, plants allocate photosynthate belowground to the bacteria in exchange for nitrogen fixed from the atmosphere. This symbiosis forms an important link between carbon and nitrogen cycles in many ecosystems. However, the economics of this relationship under soil nitrogen availability gradients is not well understood, as plant investment toward symbiotic nitrogen fixation tends to decrease with increasing soil nitrogen availability. Here, we used a manipulation experiment to examine how costs of nitrogen acquisition vary under a factorial combination of soil nitrogen availability and inoculation with Bradyrhizobium japonicum in Glycine max L. (Merr.). We found that inoculation decreased belowground biomass carbon costs to acquire nitrogen and increased total leaf area and total biomass, but these patterns were only observed under low fertilization and were the result of increased plant nitrogen uptake and no change in belowground carbon allocation. These results suggest that symbioses with nitrogen-fixing bacteria reduce carbon costs of nitrogen acquisition by increasing plant nitrogen uptake, but only when soil nitrogen is low, allowing individuals to increase nitrogen allocation to structures that support aboveground growth. This pattern may help explain the prevalence of plants capable of forming these associations in less fertile soils and provides useful insight into understanding the role of nutrient acquisition strategy on plant nitrogen uptake across nitrogen availability gradients. [ABSTRACT FROM AUTHOR]

THE ISSUE of heavy metals (HMs) contamination has become a matter of significant international concern. As a result, various techniques employed by biological systems to eliminate HMs are being examined. Specific HMs, such as cadmium, zinc, nickel, copper, and cobalt, are necessary for the physiological functions of both symbiotic and non-symbiotic nitrogen-fixing bacteria (NFB) when present in minor amounts. However, elevated levels of HM concentrations can impair the functioning of NFB and their symbiotic relationship. The present investigation focuses on how the NFB, resists the HMs toxicity and increases plant growth to assist in accomplishing crop cultivation in metal-contaminated locations. Numerous mechanisms were reviewed for HMs resistance such as organic ligands and thiols which annoy the metal ions constructing a complex and blocking cell impairment. This review summarizes that soil inoculation with HMs-resistant NFB reflects numerous beneficial effects in agricultural systems, therefore its application is considered a bioremediating tools that have economic and ecological importance. In addition, the current review discussed the role of NFB in reducing the toxic impacts of HMs on plant life. [ABSTRACT FROM AUTHOR]

Current agriculture intensifies crop cultivation to meet food demand, leading to unsustainable use of chemical fertilizers. This study investigates a few physiological and agronomic responses of common wheat following the inoculation with plant growth-promoting bacteria to reduce nitrogen inputs. A field trial was conducted in 2022–2023, in Legnago (Verona, Italy) on Triticum aestivum var. LG-Auriga comparing full (180 kg ha−1) and reduced (130 kg ha−1) N doses, both with and without foliar application at end tillering of the N-fixing bacterium Methylobacterium symbioticum. Biofertilization did not improve shoot growth, while it seldom increased the root length density in the arable layer. It delayed leaf senescence, prolonged photosynthetic activity, and amplified stomatal conductance and PSII efficiency under the reduced N dose. Appreciable ACC-deaminase activity of such bacterium disclosed augmented nitrogen retrieval and reduced ethylene production, explaining the ameliorated stay-green. Yield and test weight were unaffected by biofertilization, while both glutenin-to-gliadin and HMW-to-LMW ratios increased together with dough tenacity. It is concluded that Methylobacterium symbioticum can amplify nitrogen metabolism at a reduced nitrogen dose, offering a viable approach to reduce chemical fertilization under suboptimal growing conditions for achieving a more sustainable agriculture. Further research over multiple growing seasons and soil types is necessary to corroborate these preliminary observations. [ABSTRACT FROM AUTHOR]

This study aimed to examine the effectiveness of indigenous diazotrophic bacteria from saline paddy fields of The Northern Coastal of Pemalang in increasing N and K nutrient uptake in rice plants. This research was conducted at the Experimental Farm and Agronomy & Horticulture Laboratory, Faculty of Agriculture, Jenderal Soedirman University, Purwokerto. This study was designed using a completely randomized block design with nitrogen fixing bacteria as the treatment and repeated three times. The treatment that was tried was a type of N2-fixing bacteria consisting of control without inoculation of bacteria (P0), Acinetobacter junii (P1), Bacillus tropicus (P2), Acinetobacter schindleri (P3), Pseudomonas stutzeri (P4), Bacillus altitudinis (P5), Bacillus cereus (P6), and Bacillus subtilis (P7). The study used the culture solution method with the source of nutrition from AB Mixtm nutrient with EC set at 5.5 dSm-1, and pH 5.5-6.5. Observation variables including N uptake by rice plants were analyzed at the maximum vegetative phase using the Kjedahl method, Na and K absorption of rice plants were analyzed by diacidic extraction method and the results were measured using a flame photometer. The research data were analyzed using ANOVA, and if they were significantly different, they continued with DMRT 5%. The result showed that inoculation of rice plants with Bacillus subtilis significantly increased plant biomass, N uptake, and K uptake. Diazotrophic bacteria inoculation was able to increase the N uptake of rice plants by an average of 0.341 g/plant (104.36%), while in the control treatment it was only 0.167 g/plant. Inoculation of diazotrophic bacteria in plants under salinity stress tends to reduce Na uptake in rice plants. Inoculation of diazotropic bacteria was able to increase the average K/Na ratio of 113.31%, and this indicated that inoculation of halotolerant diazotrophic bacteria was able to increase the tolerance of rice plants to salinity stress. [ABSTRACT FROM AUTHOR]

Soil properties, including soil compaction and the nutrient content, influence the composition and functions of rhizosphere microbial communities. There is limited information on how soil compaction and phosphorus application affect phosphate-solubilizing (PSB) and nitrogen-fixing bacteria (NFB). This study aimed to examine the responses of PSB and NFB in the rhizosphere of peanut (Arachis hypogaea L.) plants under varying soil compaction and phosphorus application levels. To address this, pot experiments were conducted to assess the composition and assembly processes of rhizosphere PSB and NFB in peanut cultivar Hua Yu 22 under two soil compaction levels (T1, 1.25 g/cm3 compaction, and T2, 1.00 g/cm3 compaction) and two phosphorus (P) levels (P0, no P applied, and P1, 1.2 mM P/kg soil applied). The results showed that PSB community shifts were closely correlated with the content of soil available phosphorus, soil acid phosphatase activity, soil nitrogenase activity, and soil compaction. Additionally, the content of soil available phosphorus and soil compaction were correlated with changes in operational taxonomic units of NFB. A network analysis revealed that the complexities of PSB were significantly higher than those of NFB. A stronger negative relationship was identified among NFB communities. The assembly of PSB communities was primarily driven by drift processes, whereas NFB communities were influenced by a combination of homogenizing selection and drift. Both PSB and NFB community compositions were significantly affected by phosphorus limitations and soil compaction. These findings enhance our understanding of the impacts of soil compaction and phosphorus application on PSB and NFB communities, with implications for optimizing peanut crop production. Our results will provide reference for crop cultivation in compacted and low-phosphorus soils. The important phosphate-solubilizing and nitrogen-fixing bacteria screened in the interaction network in this study will become candidate microbial agents for alleviating soil compaction and low phosphorus levels. [ABSTRACT FROM AUTHOR]

Indiscriminate use of mineral fertilizers has a broad negative impact on soil health. Because of the above, there is an urgent need to search for natural organic alternatives, including using soil microbial resources to replenish soil nutrients for enhanced Agri productivity vis a vis sustainably maintaining soil health. The nitrogen-fixing rhizobacteria (NFR) are such type of bacteria which fix gaseous atmospheric nitrogen in the soil and in nodules of certain plant species in considerable amounts that are readily available for plants' uptake and may be considered as a viable alternative source of mineral nitrogen application. The present study was conducted to isolate the most potent nitrogen-fixing bacteria from the litchi rhizosphere. Hence, Five NFR (NFR1 to NFR5) were isolated from the rhizosphere of litchi orchard of Bihar Agricultural University, Sabour, Bhgalpur, India, based on their ability to fix atmospheric nitrogen in a nitrogen-free mineral salt medium. NFR2 was found to be the most potent in fixing atmospheric nitrogen (11.31 mg N per gram carbon source)among all the isolated rhizobacterial strains. Hence, on the basis of biological nitrogen fixation ability, the isolate NFR2 was subjected to 16S ribosomal RNA (16S rRNA) gene sequencing for molecular characterization. Based on 16S rDNA sequence analysis, NFR2 showed the closest sequence homology with Beijerinckia fluminensis and was identified and reported as Beijerinckia fluminensis strain BAUMS11, Accession number MN533953. The study noticeably indicated that the B. fluminensis strain BAUMS11 was found most efficient in fixing gaseous atmospheric nitrogen and may be used for the manufacturing of nitrogenous biofertilizer, which can fix atmospheric nitrogen to the tune-up to 30 kg N ha-1yr-1. [ABSTRACT FROM AUTHOR]

This comprehensive review investigates the potential of cyanobacteria, particularly nitrogen-fixing strains, in addressing global challenges pertaining to plastic pollution and carbon emissions. By analyzing the distinctive characteristics of cyanobacteria, including their minimal growth requirements, high photosynthetic efficiency, and rapid growth rates, this study elucidates their crucial role in transforming carbon sequestration, biofuel generation, and biodegradable plastic production. The investigation emphasizes cyanobacteria's efficiency in photosynthesis, positioning them as optimal candidates for cost-effective bioplastic production with minimized land usage. Furthermore, the study explores their unconventional yet promising utilization in biodiesel production, mitigating environmental concerns such as sulfur emissions and the presence of aromatic hydrocarbons. The resulting biodiesel exhibits significant combustion potential, establishing cyanobacteria as a viable option for sustainable biofuel production. Through a comprehensive assessment of both achievements and challenges encountered during the commercialization process, this review offers valuable insights into the diverse contributions of cyanobacteria. Its objective is to provide guidance to researchers, policymakers, and industries interested in harnessing bio-inspired approaches for structural and sustainable applications, thereby advancing global efforts towards environmentally conscious plastic and biofuel production. [ABSTRACT FROM AUTHOR]

Brazilian soils are predominantly rich in aluminum, which becomes mobile at pH < 5, affecting sensitive plants; however, some species have developed aluminum tolerance mechanisms. The purpose of this study was to compare the physiological responses of Crotalaria genus species, family Fabaceae, which have the ability to associate with nitrogen-fixing bacteria under the influence of Al3+ in the soil. The soil used was Oxisol; the experimental design was in randomized blocks in a factorial scheme (2 × 3): soil factor (available toxic aluminum content; correction of dolomitic limestone—MgCO3) and species factor (C. juncea; C. spectabilis; C. ochroleuca); cultivated within 43, 53, and 53 days, respectively, with five replications; 30 experimental samples. Mass and length, pigments, gas exchange, and changes in nitrogen metabolism were evaluated. C. juncea showed a higher concentration of amino acids in the leaves, internal carbon, and stomatal conductance in soil with Al3+, as well as higher production of ureides, allantoinic acid, allantoic acid, proteins, and amino acids in the nodules, with 78% of the Al3+ accumulation occurring in the roots. C. ochroleuca demonstrated greater shoot length and nodule number production in limed soil; in soil with Al3+, it showed a 91% increase in chlorophyll a content and 93% in carotenoids. C. spectabilis showed a 93% increase in ureide production in the leaves in soil with Al3+. [ABSTRACT FROM AUTHOR]

This study aims to isolate Nitrogen-fixing bacteria from tailing and heavy metal (HM) polluted soils and examine their effectiveness as a plant growth-promoting rhizobacteria (PGPR) to increase foxtail millet plant growth. We analyzed artisanal and small-scale gold mining (ASGM) sites in Pongkor Village, West Java, Indonesia, and identified nine areas with significant contamination of Mercury (Hg), Lead (Pb), Cadmium (Cd), Chromium (Cr), and Arsenic (As). We isolated sixteen strains of nitrogen-fixing bacteria different carbon sources. We identified three strains (3.2.h, 4.2.b, and 9.2.a) that the most robust nitrogenase activity and indole acetic acid (IAA) production. They were identified based on their molecular characteristics (16S rRNA) as Ralstonia pickettii strain LMQOTU12, Azotobacter chroococcum subsp. isscasi strain P205, and Azotobacter chroococcum subsp. isscasi strain P205. The three isolates were inoculated to foxtail millet plant grown under Andosol slightly acidic (pH 5.8), moderate nitrogen content (0.26%). The three strains isolates demonstrated significant enhancement to foxtail millet plants' growth. Improvements (compared to control) in shoot dry weight: 8% (3.2.h), 32% (4.2.b), 88% (9.2.a); longest root length: 88.71% (3.2.h), 108.90% (4.2.b), 140.16%; root dry weight: 350% (3.2.h), 450% (4.2.b), 250% (9.2.a); and root-shoot ratio 312% (3.2.h), 312% (4.2.b), 75% (9.2.a). This study demonstrates that the three strains are potential PGPRs for increasing plant growth of foxtail millet. [ABSTRACT FROM AUTHOR]

Duckweed is a future food and a source of affordable protein that has the potential to replace animal protein. This study aims to formulate a bio-fertilizer consisting of mangrove-associated bacteria to boost the growth and protein of duckweeds as a sustainable approach to increase plant-based protein yields. The culture-depending technique was performed by using Aleksandrow agar, Pikovskaya's agar, and Jensen agar to screen potassiumsolubilizing bacteria, phosphate-solubilizing bacteria and nitrogen-fixing bacteria, respectively, from mangrove soil sediments. Mangrove-associated bacteria that are close to Acinetobacter radioresistens, Brachybacterium paraconglomeratum, and Enterobacter cloacae, which are known as nitrogen-fixing bacteria, Klebsiella quasipneumoniae, Bacillus tropicus, and Paenibacillus pasadenensis known as potassium-solubilizing bacteria, and Bacillus cereus and Bacillus thuringiensis known as phosphate-solubilizing bacteria were identified through 16S rRNA gene sequencing. After that, three sets of biofertilizers were randomly formulated. Each set consisted of nitrogen-fixing bacteria, potassium- and phosphate-solubilizing bacteria, as well as commercial compost as a carrier. These formulated bio-fertilizers were evaluated for plant growth promotion and protein production on duckweed plants under temperatures between 26 and 30°C. The results showed that each set of our formulated bio-fertilizer can increase the nitrogen (N), phosphorus (P), and potassium (K), duckweed growth, and protein content when compared to the control group. It indicates that bio-fertilizers formulated with mangrove-associated bacteria and high NPK contents could enhance the growth of duckweed as well as its protein content, which could supply our future plant-based protein sustainably. [ABSTRACT FROM AUTHOR]

Modified clay granules were used to promote Azotobacter vinelandii cell adhesion. The A. vinelandii cells in the clay granules were used as a biofertilizer and a plant material. The production process was carried out under variable temperatures. The raw ingredients consisted of clay, sawdust waste, and spent coffee grounds in different ratios. Scanning electron microscopy (SEM) was used to analyze the microstructure. The results of the study showed the addition of sawdust waste and spent coffee grounds had increased the water absorption of the fired clay granules based on their porosity. However, increasing the firing temperature in the range of 900°C - 1100°C decreased the water absorption and porosity and increased the bulk density of the fired clay granules. A. vinelandii was enriched to be used as a cell suspension. The fired clay granules were immersed in a cell suspension to immobilize the A. vinelandii cells for 48 h. The SEM-based investigations indicated that the fired clay granules were suitable for containing A. vinelandii cells. The results demonstrated high viability of bacterial cells fixed in the fired clay granules at 2.7× 107 CFU/g. Furthermore, the test results of bacterial cells in the fired clay granules for marigold planting media revealed that it had effectively encouraged plant growth. The nitrogen-fixing bacterial cells in the clay granules obtained from this research were determined to be appropriate for use as an ecological soil replacement in the future. [ABSTRACT FROM AUTHOR]

In oligotrophic oceans, primary productivity is widely limited by nitrogen bioavailability. The broadly distributed and abundant nitrogen-fixing cyanobacterium Trichodesmium plays an important role in the oceanic nitrogen and carbon cycles by providing a "new" source of nitrogen to many non-diazotrophic microbes, thereby driving new primary production in the ocean. However, the underlying process and mechanism of nitrogen supply from Trichodesmium to other phytoplankton remain unclear. Here, our results demonstrated that the fixed nitrogen released by Trichodesmium could sustain the growth of a non-nitrogen-fixing cyanobacterium Synechococcus sp. PCC 7002, including a mutant strain (Mut-ureA) that cannot use urea. However, the growth rate of Mut-ureA was approximately 20% lower than that of the wild strain when Trichodesmium filtrate was used for nitrogen supply. This result was consistent with the composition of the Trichodesmium exudate, in which urea comprised more than 20% of the total fixed nitrogen that was released. It is evident from the experiments that a fraction of the Trichodesmium-derived nitrogen was not available to Mut-ureA. Our results suggested that Trichodesmium produces dissolved organic nitrogen, especially a certain amount of urea as a "new" nitrogen source, benefiting in particular populations of surrounding phytoplankton species. [ABSTRACT FROM AUTHOR]

Host plants benefit from legume root nodule symbiosis with nitrogen-fixing bacteria under nitrogen-limiting conditions. In this interaction, the hosts must regulate nodule numbers and distribution patterns to control the degree of symbiosis and maintain root growth functions. The host response to symbiotic bacteria occurs discontinuously but repeatedly at the region behind the tip of the growing roots. Here, live-imaging and transcriptome analyses revealed oscillating host gene expression with approximately 6-hour intervals upon bacterial inoculation. Cytokinin response also exhibited a similar oscillation pattern. Cytokinin signaling is crucial to maintaining the periodicity, as observed in cytokinin receptor mutants displaying altered infection foci distribution. This periodic regulation influences the size of the root region responsive to bacteria, as well as the nodulation process progression. [ABSTRACT FROM AUTHOR]

Cyanobacteria of the genus Trichodesmium form extensive blooms that supply new N to nutrient-poor marine ecosystems. Yet little is known about what eats Trichodesmium. In this laboratory study, we show that one of the greatest threats to coral reefs, predatory crown-of-thorns starfish (CoTS), Acanthaster sp., completes their larval phase feeding solely on Trichodesmium. We observed Trichodesmium erythraeum CMP1985 in the stomachs of larvae using florescence microscopy and traced the assimilation of nitrogen from labeled trichomes into larval tissues using stable isotopes. Some larvae fed T. erythraeum were morphologically ready to become benthic juveniles after 19 days. Given that Trichodesmium can be food for CoTS, reported increases in Trichodesmium could be a driving factor in the heightened frequency of CoTS population irruptions that have devastated coral reefs in past decades. Future studies could test this through investigating the diets of wild larvae and incorporating Trichodesmium abundance into models of CoTS population dynamics. [ABSTRACT FROM AUTHOR]

Background: The excessive application of chemical fertilizers in the cultivation of Astragalus mongholicus Bunge results in a reduction in the quality of the medicinal plant and compromises the sustainable productivity of the soil. PGPB inoculant is a hot topic in ecological agriculture research. In the cultivation of Astragalus mongholicus, the screened nitrogen-fixing bacteria can promote plant growth, however, whether it can promote the accumulation of main bioactive components remains unknown. In this study, mixed inoculants containing 5 strains of growth promoting bacteria (Rhizobium T16, Sinorhizobium T21, Bacillus J1, Bacillus G4 and Arthrobacter J2) were used in the field experiment. The metabolic substances in the root tissues of Astragalus mongholicus were identified during the harvest period by non-targeted metabolomics method, and the differential metabolites between groups were identified by statistical analysis. Meanwhile, high-throughput sequencing was performed to analyze the changes of rhizosphere soil and endophytic microbial community structure after mixed microbial treatment. Results: The results of non-targeted metabolism indicated a significant increase in the levels of 26 metabolites after treatment including 13 flavonoids, 3 saponins and 10 other components. The contents of three plant hormones (abscisic acid, salicylic acid and spermidine) also increased after treatment, which presumed to play an important role in regulating plant growth and metabolism. Studies on endosphere and rhizosphere bacterial communities showed that Rhzobiaceae, Micromonosporaceae, and Hypomicrobiaceae in endophytic, and Oxalobactereae in rhizosphere were significantly increased after treatment. These findings suggest their potential importance in plant growth promotion and secondary metabolism regulation. Conclusions: This finding provides a basis for developing nitrogen-fixing bacteria fertilizer and improving the ecological planting efficiency of Astragalus mongholicus. [ABSTRACT FROM AUTHOR]

Plant-parasitic nematodes (PPNs) are among the most damaging pathogens to host plants. Plants can modulate their associated bacteria to cope with nematode infections. The tritrophic plant-nematode-microbe interactions are highly taxadependent, resulting in the effectiveness of nematode agents being variable among different host plants. Ficus tikoua is a versatile plant with high application potential for fruits or medicines. In recent years, a few farmers have attempted to cultivate this species in Sichuan, China, where parasitic nematodes are present. We used 16S rRNA genes to explore the effects of nematode parasitism on rootassociated bacteria in this species. Our results revealed that nematode infection had effects on both endophytic bacterial communities and rhizosphere communities in F. tikoua roots, but on different levels. The species richness increased in the rhizosphere bacterial communities of infected individuals, but the community composition remained similar as compared with that of healthy individuals. Nematode infection induces a deterministic assembly process in the endophytic bacterial communities of parasitized organs. Significant taxonomic and functional changes were observed in the endophytic communities of root knots. These changes were characterized by the enrichment of nitrogen-fixing bacteria, including Bradyrhizobium, Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium, and nematode-antagonistic bacteria, such as Pseudonocardia, Pseudomonas, Steroidobacter, Rhizobacter, and Ferrovibrio. Our results would help the understanding of the tritrophic plant-nematode-bacterium interactions in host plants other than dominant crops and vegetables and would provide essential information for successful nematode management when F. tikoua were cultivated on large scales. [ABSTRACT FROM AUTHOR]

Premise Methods Results Conclusions Legumes establish mutualistic interactions with pollinators and nitrogen (N)‐fixing bacteria that are critical for plant reproduction and ecosystem functioning. However, we know little about how N‐fixing bacteria and soil nutrient availability affect plant attractiveness to pollinators.In a two‐factorial greenhouse experiment to assess the impact of N‐fixing bacteria and soil types on floral traits and attractiveness to pollinators in Chamaecrista latistipula (Fabaceae), plants were inoculated with N‐fixing bacteria (NF+) or not (NF‐) and grown in N‐rich organic soil (+N organic soil) or N‐poor sand soil (‐N sand soil). We counted buds and flowers and measured plant size during the experiment. We also measured leaf, petal, and anther reflectance with a spectrophotometer and analyzed reflectance curves. Using the bee hexagon model, we estimated chromatic contrasts, a crucial visual cues for attracting bees that are nearby and more distant.NF+ plants in ‐N sand soil had a high floral display and color contrasts. On the other hand, NF‐ plants and/or plants in +N organic soil had severely reduced floral display and color contrasts, decreasing floral attractiveness to bee pollinators.Our findings indicate that the N‐fixing bacteria positively impact pollination, particularly when nutrients are limited. This study provides insights into the dynamics of plant–pollinator interactions and underscores the significant influence of root symbionts on key floral traits within tropical ecosystems. These results contribute to understanding the mechanisms governing mutualisms and their consequences for plant fitness and ecological dynamics. [ABSTRACT FROM AUTHOR]

Ferruginicity is a special condition when soil became rich in iron. This condition is characterized by high pH and reduced bioavailability of plant limiting nutrients. Unfortunately, this type of soil covered 30% of arable lands in Nigeria. This research aimed at using a native plant growth promoting bacteria (Bacillus cereus strain GGBSU-1, Klebsiella variicola strain AUH-KAM-9 and Proteus mirabilis strain TL14-1) with phosphate solubilizing capabilities to remediate iron toxicity and improve soil nutrients, as well as soil micro-biota colonization. Soil physico-chemical properties before rhizo-inoculation (FA), after 16 weeks of rhizoinoculation with the PGPB into the rhizoid of a growing rice seedling (FB) and after 16 weeks of natural attenuation (FC) were analyzed. Phosphate solubilizing capacity of the PGPB was investigated using a developed Pikovskaya’s growth medium. The results showed that FA is rich in iron and deficient in bioavailable phosphorus and nitrogen (200.67 mg/kg, 8.01 mg/kg and 0.20%) respectively, as against the FB soil which showed moderate iron and increased soil nutrients (51.22 mg/kg, 20.21 mg/kg and 0.33%). The presence of acidic exudates, which was indicated by a red litmus paper at the rhizosphere in FB signifies the iron chelation capacity of the PGPBs resulting in iron remediation and soil nutrient improvement. Furthermore, the significant increase in microbial population in the FB soil as against the FA and FC corresponds with the SEM results at the root epidermis. Furthermore, other nitrogen-fixing bacteria such as Bacillus subtilis were observed to be active and motile in the FB. This indicated the effectiveness of PGPB with PSB capacities in iron remediation and soil nutrient enhancement. [ABSTRACT FROM AUTHOR]

This paper presents the first in-depth research on the biological and genomic properties of lytic rhizobiophage AP-J-162 isolated from the soils of the mountainous region of Dagestan (North Caucasus), which belongs to the centers of origin of cultivated plants, according to Vavilov N.I. The rhizobiophage host strains are nitrogen-fixing bacteria of the genus Sinorhizobium spp., symbionts of leguminous forage grasses. The phage particles have a myovirus virion structure. The genome of rhizobiophage AP-J-162 is double-stranded DNA of 471.5 kb in length; 711 ORFs are annotated and 41 types of tRNAs are detected. The closest phylogenetic relative of phage AP-J-162 is Agrobacterium phage Atu-ph07, but no rhizobiophages are known. The replicative machinery, capsid, and baseplate proteins of phage AP-J-162 are structurally similar to those of Escherichia phage T4, but there is no similarity between their tail protein subunits. Amino acid sequence analysis shows that 339 of the ORFs encode hypothetical or functionally relevant products, while the remaining 304 ORFs are unique. Additionally, 153 ORFs are similar to those of Atu_ph07, with one-third of the ORFs encoding different enzymes. The biological properties and genomic characteristics of phage AP-J-162 distinguish it as a unique model for exploring phage–microbe interactions with nitrogen-fixing symbiotic microorganisms. [ABSTRACT FROM AUTHOR]

Increased nitrogen deposition is a key feature of global climate change, however, its effects on the structure and assembling mechanisms of the nitrogen-fixing bacteria present at the root surface remain to be elucidated. In this pursuit, we used NH4NO3 to simulate nitrogen deposition in a 10-year-old Camellia oleifera plantation, and set up four deposition treatments, including control N0 (0 kg N hm-2 a-1), low nitrogen N20 (20 kg N hm-2 a-1), medium nitrogen N40 (40 kg N hm-2 a-1) and high nitrogen N160 (160 kg N hm-2 a-1). The results showed that nitrogen deposition affected the soil nitrogen content and the structure of the nitrogen-fixing bacterial community. Low nitrogen deposition was conducive for nitrogen fixation in mature C. oleifera plantation. With increasing nitrogen deposition, the dominant soil nitrogen-fixing bacterial community shifted from Desulfobulbaceae to Bradyrhizobium. When nitrogen deposition was below 160 kg N hm-2 a-1, the soil organic matter content, total nitrogen content, nitrate nitrogen content, ammonium nitrogen content, urease activity, soil pH and nitrate reductase activity influenced the composition of the nitrogen-fixing bacterial community, but the stochastic process remained the dominant factor. The results indicate that the strains of Bradyrhizobium japonicum and Bradyrhizobium sp. ORS 285 can be used as indicator species for excessive nitrogen deposition. [ABSTRACT FROM AUTHOR]

The combined use of endophytic nitrogen-fixing bacteria (ENFB) and organic manures is a trend in sustainable agricultural production. To investigate the effect of Enterobacter asburiae (E asburiae) and vermicompost (VCT) on farmland nutrients, yield, quality, and reduce arsenic uptake of peanuts. Three factors, which were: (i) E asburiae (inoculum and no inoculum); (ii) irrigation water (River and underground water); (iii) VCT (0.00 and 10.0 t ha-1), were designed by eight treatments (Trt) and four replications. E asburiae inoculation combined with 10 t VCT ha-1 application and river water (RW) irrigation that both raised soil nutrient properties and traits of peanut agronomy and yield traits, raised significantly fresh seed yield and reduced arsenic (As) absorption of peanut stems and seeds. fresh seed yield of peanut in treatments of E asburiae inoculation, RW irrigation and 10.0 t VCT ha-1, which were higher than non E asburiae inoculation, deep well water (DWW) irrigation and no VCT application, were 24.3, 26.9 and 15.4%, respectively. The peanut As contents in Trt of E asburiae inoculation, RWI and 10.0 t VCT ha-1 were lower than 7.78, 45.3 and 1.92% in stems and 13.2, 78.3 and 9.82% in seeds, respectively, compared to non-E asburiae inoculation, DWW irrigation and no VCT application. E asburiae was found out one potential species to promote soil nutrients, the peanut growth, yield, quality and As resistance, which will be used like biological fertilizers in the future. [ABSTRACT FROM AUTHOR]

Comprehensive assessment of sowing qualities of soybean seeds after pre-sowing treatment of seeds with biological preparations is a scientifically valuable and urgent problem of today, which made it possible to choose the optimal methods of realizing the genetic potential of productivity of modern soybean varieties. In laboratory and vegetation conditions, the sowing properties of soybean seeds were evaluated under pre-sowing seed sterilization. The aim of the research was to establish the sowing qualities of soybean seeds (varieties Slavna, Churaivna, Azymut, Tytan, Triada, Pallada, Samorodok), namely seed moisture, germination energy, field germination and linear hypocotyl parameters depending on the varietal composition and pre-sowing seed treatment with a bacterial preparation. Field and laboratory studies were conducted according to the following indicators: seed moisture, germination energy, field germination and linear hypocotyl parameters according to generally accepted methods. Research on the basis of the scientific research field of the Institute of Fodder and Agriculture of the Podillia National Academy of Sciences by the method of split plots in four repetitions according to the methodology of research in agronomy, p. Bohonyky, Vinnytsia region, Ukraine. It was established that the moisture content of the seeds of soybean varieties during 2020-2023 storage in uncontrolled climate conditions was within the normal range and did not exceed 13.4%. It was noted that the use of pre-sowing treatment of seeds with a bacterial preparation based on strains of nodule bacteria had a smaller effect on laboratory germination, and to a greater extent on the germination energy of soybean seeds. The maximum indicator was obtained on the Slavna soybean variety - 93.4% for the use of nitrogen-fixing bacteria (Rhizoline+Rhizosave) in the presowing treatment of seeds. Laboratory germination had a significant tendency to increase up to 96.3-98.1% in variants with Svavna and Tytan varieties for the use of nitrogen-fixing bacteria (Rizolain+Rhizosave) in the presowing seed treatment. Based on the obtained results, in order to stimulate the germination of soybean seeds, it is proposed to bacteriize them with complex inoculants, which is a more effective measure than inoculation with a monoculture of rhizobia. In the conditions of the Right Bank Forest-Steppe, in the variants where a bacterial preparation (Rizolain+Rhizosev) was used for pre-sowing seed treatment, the mentioned technological methods of growing can be used to improve the technology of growing soybeans. [ABSTRACT FROM AUTHOR]

Saffron (Crocus sativus L.), a bulbous and perennial plant, is highly influenced by environmental factors such as light, moisture, temperature, and nutrition, which can significantly affect its growth and development. To investigate the effects of different biofertilizers and irrigation regimes on the characteristics of saffron corms and flowers, an experiment was conducted over two agricultural years (2021-2022 and 2022-2023) in the agricultural lands of Ziar city, a suburb of Isfahan. This experiment was carried out as split plots based on randomized complete block design with three replications. The main factor was deficit irrigation at three levels (50%, 75%, and 100% of the crop water requirement), and the sub-factors included eight levels: nitrogen-fixing free-living bacteria (B-N), potassiumsolubilizing bacteria (B-K), phosphate-solubilizing bacteria (B-P), their combination, and a control with no fertilizer. The results indicated that the highest number of corms (415 m-2), corm weight (2360 g. m-2), corm without scales belonged weight (2304 g. m-2), number of corms weighing 0-4 grams (244 m-2), number of corms weighing 4-8 grams (135 m-2), number of corms weighing 8-12 grams (55.3 m-2), number of corms weighing over 12 grams (64.2 m-2), dry stigma weight (0.492 g. m-2), and dry style weight (0.122 g. m-2) were obtained from the treatment with 100% water requirement and NPK biofertilizer combination. Ultimately, the best treatment for optimal performance was 100% water requirement combined with NPK biofertilizer. [ABSTRACT FROM AUTHOR]

Increasing the soybean-planting area and increasing the soybean yield per unit area are two effective solutions to improve the overall soybean yield. Northeast China has a large saline soil area, and if soybeans could be grown there with the help of isolated saline-tolerant rhizobia, the soybean cultivation area in China could be effectively expanded. In this study, soybeans were planted in soils at different latitudes in China, and four strains of rhizobia were isolated and identified from the soybean nodules. According to the latitudes of the soil-sampling sites from high to low, the four isolated strains were identified as HLNEAU1, HLNEAU2, HLNEAU3, and HLNEAU4. In this study, the isolated strains were identified for their resistances, and their acid and saline tolerances and nitrogen fixation capacities were preliminarily identified. Ten representative soybean germplasm resources in Northeast China were inoculated with these four strains, and the compatibilities of these four rhizobium strains with the soybean germplasm resources were analyzed. All four isolates were able to establish different extents of compatibility with 10 soybean resources. Hefeng 50 had good compatibility with the four isolated strains, while Suinong 14 showed the best compatibility with HLNEAU2. The isolated rhizobacteria could successfully establish symbiosis with the soybeans, but host specificity was also present. This study was a preliminary exploration of the use of salinity-tolerant rhizobacteria to help the soybean nitrogen fixation in saline soils in order to increase the soybean acreage, and it provides a valuable theoretical basis for the application of saline-tolerant rhizobia.

Simple Summary: The sustainability of the tomato industry is increasingly debatable, necessitating innovative approaches to maximize productivity while minimizing environmental impact. The exploration of Synthetic Communities (SynComs) comprising nitrogen-fixing bacteria and mycorrhizal fungi represents a promising avenue toward achieving this balance. This work demonstrates that SynComs not only support tomato production under reduced fertilizer inputs, but also contribute to enhancing soil microbial biodiversity. This dual benefit underscores the potential of SynComs as a soil management strategy, offering a pathway toward sustainable agriculture and environmental stewardship. The agricultural sector is currently encountering significant challenges due to the effects of climate change, leading to negative consequences for crop productivity and global food security. In this context, traditional agricultural practices have been inadequate in addressing the fast-evolving challenges while maintaining environmental sustainability. A possible alternative to traditional agricultural management is represented by using beneficial micro-organisms that, once applied as bioinoculants, may enhance crop resilience and adaptability, thereby mitigating the adverse effects of environmental stressors and boosting productivity. Tomato is one of the most important crops worldwide, playing a central role in the human diet. The aim of this study was to evaluate the impact of a nitrogen-fixing bacterial-based biostimulant (Azospirillum sp., Azotobacter sp., and Rhizobium sp.) in combination or not with a commercial inoculum Micomix (Rhizoglomus irregulare, Funnelliformis mosseae, Funnelliformis caledonium, Bacillus licheniformis, and Bacillus mucilaginosus) (MYC) on the native rhizosphere communities and tomato production. Bacterial populations in the different samples were characterized using an environmental metabarcoding approach. The bioinocula effect on the native rhizosphere microbiota resulted in significant variation both in alpha and beta diversity and in a specific signature associated with the presence of biostimulants. [ABSTRACT FROM AUTHOR]

Soybean [Glycine max (L.) Merr.] is one of the most important and oldest crops. Due to its ability to form symbiotic interactions with nitrogen-fixing bacteria, it is a valuable source of nitrogen for agriculture and proteins for humans and livestock. In Europe, for instance, in Poland, the soybean cultivation area is still not large but is gradually increasing due to climate change. The lack of indigenous soybean microsymbionts in Polish soils forces the application of commercial strains to establish effective symbioses. Fast and reliable identification methods are needed to study the persistence, competitiveness, and dispersal of bradyrhizobia introduced as inocula. Our study aimed to apply real-time PCR coupled with high-resolution melting curve (HRM) analysis to detect and differentiate bacterial strains occupying soybean nodules. HRM-PCR was performed on crude extracts from nodules using primers specific for recA, a highly conserved nonsymbiotic gene. By comparing them with the reference strains, we were able to identify and assign Bradyrhiobium strains that had been introduced into field locations in Poland. In conclusion, HRM analysis was proven to be a fast and accurate method for identifying soybean microsymbionts and might be successfully used for identifying other legume-nodulating bacteria. [ABSTRACT FROM AUTHOR]

Regular application of synthetic chemicals in rice ecosystem led to loss of nitrogen (N) and affected the native microbial communities. Controlled release fertilizers (CRFs), a solution to poor nitrogen use efficiency (NUE) of urea and associated environmental implications while diminished economic advantages by high CRF use, is major obstacle that still exists. Reviving the diazotrophic native bacteria from rice cultivated locations should be the alternate for bounciness of potential bioinoculants for better performance and yield enhancement. In the present investigation, two potential nitrogen fixing bacteria, Pseudomonas lini GHM32 and Brevundimonas nasdae GHM62 isolated from rice rhizosphere on Rennie medium. These two bacteria were evaluated for yield and NUE in field studies in a randomized block design with treatments, T1- 100% recommended dose of nitrogen through neem coated urea (RDN), T2- 50% RDN, T3- 50% RDN + P. lini GHM32, T4- 50% RDN + B. nasdae GHM62 and T5- co-application of both bacterial isolates during Rabi-2020-21 (dry season) and Kharif-2021 (wet season). Experimental results for plant height, chlorophyll, nitrogen content and yield in T3 were on par T1. Nitrogen use efficiency indices, such as partial factor productivity (PFP), nitrogen use efficiency (NUE) and nitrogen requirement (NR) of T3 were at par T1 throughout the experimental period. This is the first report with field trials on P. lini and B. nasdae as potential diazotrophic bacterial application by reduction in application of inorganic N fertilizer through neem coated urea with a focus on NUE indices and yield improvement of rice. [ABSTRACT FROM AUTHOR]

Tuber magnatum is the most expensive truffle, but its large‐scale cultivation is still a challenge compared to other valuable Tuber species. T. magnatum mycelium has never been grown profitably until now, which has led to difficulties to studying it in vitro. This study describes beneficial interactions between T. magnatum mycelium and never before described bradyrhizobia, which allows the in vitro growth of T. magnatum mycelium. Three T. magnatum strains were co‐isolated on modified Woody Plant Medium (mWPM) with aerobic bacteria and characterised through microscopic observations. The difficulties of growing alone both partners, bacteria and T. magnatum mycelium, on mWPM demonstrated the reciprocal dependency. Three bacterial isolates for each T. magnatum strain were obtained and molecularly characterised by sequencing the 16S rRNA, glnII, recA and nifH genes. Phylogenetic analyses showed that all nine bacterial strains were distributed among five subclades included in a new monophyletic lineage belonging to the Bradyrhizobium genus within the Bradyrhizobium jicamae supergroup. The nifH genes were detected in all bacterial isolates, suggesting nitrogen‐fixing capacities. This is the first report of consistent T. magnatum mycelium growth in vitro conditions. It has important implications for the development of new technologies in white truffle cultivation and for further studies on T. magnatum biology and genetics. [ABSTRACT FROM AUTHOR]

The symbiotic relationship between nitrogen-fixing cyanobacteria and plants offers a promising avenue for sustainable agricultural practices and environmental remediation. This review paper explores the molecular interactions between nitrogen-fixing cyanobacteria and nanoparticles, shedding light on their potential synergies in agricultural nanotechnology. Delving into the evolutionary history and specialized adaptations of cyanobacteria, this paper highlights their pivotal role in fixing atmospheric nitrogen, which is crucial for ecosystem productivity. The review discusses the unique characteristics of metal nanoparticles and their emerging applications in agriculture, including improved nutrient delivery, stress tolerance, and disease resistance. It delves into the complex mechanisms of nanoparticle entry into plant cells, intracellular transport, and localization, uncovering the impact on root-shoot translocation and systemic distribution. Furthermore, the paper elucidates cellular responses to nanoparticle exposure, emphasizing oxidative stress, signaling pathways, and enhanced nutrient uptake. The potential of metal nanoparticles as carriers of essential nutrients and their implications for nutrient-use efficiency and crop yield are also explored. Insights into the modulation of plant stress responses, disease resistance, and phytoremediation strategies demonstrate the multifaceted benefits of nanoparticles in agriculture. Current trends, prospects, and challenges in agricultural nanotechnology are discussed, underscoring the need for responsible and safe nanoparticle utilization. By harnessing the power of nitrogen-fixing cyanobacteria and leveraging the unique attributes of nanoparticles, this review paves the way for innovative, sustainable, and efficient agricultural practices. [ABSTRACT FROM AUTHOR]

In the genome of the heterocystous cyanobacterium Calothrix sp. NIES-4101 (NIES-4101), the four genes essential for nitrogen fixation (nifB, nifH, nifD and nifK) are highly fragmented into 13 parts in a 350-kb chromosomal region, and four of these parts are encoded in the reverse strand. Such a complex fragmentation feature makes it difficult to restore the intact nifBHDK genes by the excision mechanism found in the nifD gene of the Anabaena sp. PCC 7120 heterocyst. To examine the nitrogen-fixing ability of NIES-4101, we confirmed that NIES-4101 grew well on a combined nitrogen-free medium and showed high nitrogenase activity, which strongly suggested that the complete nifBHDK genes are restored by a complex recombination process in heterocysts. Next, we resequenced the genome prepared from cells grown under nitrogen-fixing conditions. Two contigs covering the complete nifHDK and nifB genes were found by de novo assembly of the sequencing reads. In addition, the DNA fragments covering the nifBHDK operon were successfully amplified by PCR. We propose that the process of nifBHDK restoration occurs as follows. First, the nifD–nifK genes are restored by four excision events. Then, the complete nifH and nifB genes are restored by two excision events followed by two successive inversion events between the inverted repeat sequences and one excision event, forming the functional nif gene cluster, nifB-fdxN-nifS-nifU-nifH-nifD-nifK. All genes coding recombinases responsible for these nine recombination events are located close to the terminal repeat sequences. The restoration of the nifBHDK genes in NIES-4101 is the most complex genome reorganization reported in heterocystous cyanobacteria. [ABSTRACT FROM AUTHOR]

[Objective] The paper aimed to study the effects of biochar application on the quality of cured tobacco, soil mutrients and soil microbial community structure. (Method) A randomised block group field experiment was conducted using Yunyan 87 as the experimental mate rial. Four treatments were set up (SWT1: Conventional fertilization; SWT2: Conventional fertilization biochar 1500 kg/hm²; SWT3: Conventional fertilization + biochar 2250 kg/hm²; SWT4: Conventional fertilization biochar 3000 kg/hm²) to determine the chemical composition, sensory quality of cured tobacco and the soil nutrients, rhizosphere soil hacterial diversity of the cured tobacco at maturity. [Result] The application of biochar had no significant influence on the soil nutrients and chemical composition of cured tobacco. Compared with the SWTI treatment, the sensory quality of cured tobacco was significantly improved in all treatments of biochar application, among which SWT3 treat- ment showed the best performance with 13.85%,6.56%,10.87%,8.70%,4.62%,12.31% and 6.25% improvement in amma quality, aroma amount, concentration, strength, impurities, usage value, and total score, respectively. With the increase of biochar application rate, the bacterial richness (Chaol index), diversity (Shannon indes), total ASV number and unique ASV number in the rhizosphere soil of flue- cured tobacco showed a decreasing trend. Compared with SWT1 treatment, the difference in microbial community structure composition incre aed with the increase of biochar application rate. The dominant phyla of each treatment were Proteobacteria, Acidobacteria and Actinobacte ria, At the phylum classification level, there was no significant difference in the community structure composition among different treatments. The application of biochar increased the relative abundance of f Rhizobiaceae, g Allorhizobium, Neorhizobium, g Pararhizobium, g Rhizobium and other nitrogen fixing bacteria, as well as funcultured_Actinobacterium, f Burkholderiaceae, Pseudomonadaceae, o Pseudomonadale, g Pseudomonas, g Sphingopyxis, & Dyella, g Massilin and other growth promoting bacteria. The application of biochar decreased the relative abundance of denitrifying bacteria such as sunclassified_Anaerolinencrar and g unclassified Caulobacteracene. At the ASV classification level, AN was the dominant factor affecting the changes in soil bacterial community structure. [Conclusion] The application of biochar improve the sensory quality of cured tobacco leaves, with SWT3 treatment (2250 kg/hm²) performing the best. The application of biochar reduce thizosphere soil bacteria a-diversity, and increase the relative abundance of beneficial hacteria such as nitrogen fixing bacteria, growth promoting bacteria, and denitrifying bacteria in the thizosphere soil, which is beneficial for increasing soil nutrients and promoting plant growth. [ABSTRACT FROM AUTHOR]

The health of soil is paramount for sustaining life, as it hosts diverse communities of microorganisms that interact with plants, influencing their growth, health, and resilience. Beneficial microorganisms, including fungi and bacteria, form symbiotic relationships with plants, providing essential nutrients, promoting growth, and enhancing stress tolerance. These microorganisms, such as mycorrhizal fungi and plant growth-promoting bacteria, play crucial roles in nutrient cycling, soil health, and plant productivity. Additionally, they help lessen reliance on chemical fertilizers, thereby mitigating the environmental risks associated with their use. Advances in agricultural practices harness the potential of these beneficial microorganisms to improve crop yields while minimizing the environmental impact. However, challenges such as competition with indigenous microbial strains and environmental factors limit the universal utilization of microbial inoculants. Despite these challenges, understanding and leveraging the interactions between plants and beneficial microorganisms hold promise for sustainable agriculture and enhanced food security. [ABSTRACT FROM AUTHOR]

Given the importance of biological nitrogen (N) fixation in agroecosystems, using inoculants with phyllosphere N fixers effective across various crops would revolutionize agriculture. In this study, the application of an inoculant prepared from Methylobacterium symbioticum was tested on young olive trees. The pot experiment was arranged in a factorial design, with inoculant (Yes and No) and mineral N applied to the soil [0 (N0), 25 (N25), 50 (N50), and 100 (N100) kg ha−1], and four replicates. The inoculant application did not increase plant dry matter yield (DMY), whereas the application of mineral N had a significant and pronounced effect. The inoculant also did not significantly increase N concentration in tissues, unlike the strong increase observed with N applied to the soil. The inoculant significantly increased plant N recovery, a cumulative effect resulting from small increases in DMY and N concentration in tissues. This increase represented 5.2% more N in plants receiving the inoculant compared to untreated ones. However, only treatments receiving mineral N recorded positive values of fixed N, with the highest value observed in the N50 treatment (12.4%), whereas a negative value (−7.7%) was observed in the N0 treatment. Overall, these low values of fixed N question the economic rationale of using this inoculant by farmers and especially render it unsuitable for organic farming systems, where plants tend to have lower N levels in tissues. [ABSTRACT FROM AUTHOR]

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The Sustainable Development Goal 2 of the United Nations towards 2030 aimed to end hunger, achieve food security and improved nutrition, and promote sustainable agriculture. According to the 2023 report by the Food and Agriculture Organization, the world is not on track to end hunger or promote sustainable agriculture by that time. Climate change acts as a "crisis multiplier", resulting in lower food productivity and higher prices, contributing further to poverty, hunger, and instability. The number of undernourished people in drought-sensitive and low-income regions of the world has increased this decade. In this review, we analyze the potential of microalgae and cyanobacteria to aid conventional agriculture in providing critical services such as carbon capture, wastewater management, food/feed, biofuels, and other higher value bioproducts. Specifically, we focus on the use of filamentous N2-fixing cyanobacteria for providing those benefits, even in semidry regions of the world with limited access to affordable nitrogen fertilizers to boost crop productivity. We comprehensively consider the eco-physiological basis of this potential, and the available alternative technologies for large-scale biomass production. We analyze venues for filamentous N2-fixing cyanobacteria applications in standalone processes, or integrated into more complex industrial symbioses, towards increased crop productivity, and water and N-fertilizer use efficiency. Throughout the text, we highlight aspects which still require further optimization, or technological breakthroughs, for full realization of the potential of filamentous N2-fixing cyanobacteria for contributing to Sustainable Development Goals. [ABSTRACT FROM AUTHOR]

Diazotrophic communities contribute inorganic nitrogen for the primary productivity of the marine environment by biological nitrogen fixation (BNF). They play a vital role in the biogeochemical cycle of nitrogen in the marine ecological environment. However, there is still an incomplete understanding of BNF and diazotrophs in artificial seaweed farms. Therefore, this study comprehensively investigated the temporal variations of BNF associated with Gracilariopsis lemaneiformis, as well as the diazotrophic communities associated with macroalgae and its surrounding seawater. Our results revealed that a total of 13 strains belonging to Proteobacteria and Bacteroidetes were identified as N2-fixing bacteria using azotobacter selective solid medium and nifH gene cloning. Subsequently, BNF and diazotrophic communities were characterized using the acetylene reduction method and high-throughput sequencing of the nifH gene, respectively. The results showed that nitrogenase activity and nifH gene abundance of epiphytic bacteria on G. lemaneiformis varied significantly among four different cultivation periods, i.e., Cultivation Jan. (CJ), Cultivation Feb. (CF), Cultivation Mar. (CM), Cultivation Apr. (CA). Among them, the nitrogenase activity and nifH gene abundance of epiphytic bacteria on G. lemaneiformis in CM were significantly higher than those in CJ, CF, and CA, indicating that the BNF of eiphytic bacteria on G. lemaneiformis wasmarkedly enhanced. Combined with the data on environmental factors, it was found that the low concentration of nitrogen and phosphorus in CM might considerably boost the BNF of epiphytic bacteria in G. lemaneiformis. The sequencing results of the nifH gene showed that the adiversity of diazotrophic communities associated with G. lemaneiformis and seawater in CM was higher than that in other cultivation periods. In addition, the diazotrophic communities on G. lemaneiformis were significantly different in CJ, CF, CM, and CA, and they were significantly diverse from diazotrophic communities in seawater. LEfSe analysis indicated that Rhodobacterales, Hyphomonadaceae, Robiginitomaculum, and Robiginitomaculum antarcticum within a-proteobacteria played a remarkable role in BNF in response to nitrogen nutrient deficiency. Taken together, these results provide a unique insight into the interaction between macroalgae and its epiphytic bacteria and lay a foundation for further research on the mechanism of action of nitrogen-cycling microorganisms associated with macroalgae. [ABSTRACT FROM AUTHOR]

Microbes living inside or around sugarcane (Saccharum spp.) are crucial for their resistance to abiotic and biotic stress, growth, and development. Sequences of microbial genomes and genes are helpful to understand the function of these microbes. However, there is currently a lack of such knowledge in sugarcane. Here, we combined Nanopore and Illumina sequencing technologies to successfully construct the first high-quality metagenome-assembled genomes (MAGs) and gene catalogues of sugarcane culturable microbes (GCSCMs), which contained 175 species-level genome bins (SGBs), and 7,771,501 non-redundant genes. The SGBs included 79 novel culturable bacteria genomes, and 3 bacterial genomes with nitrogen-fixing gene clusters. Four single scaffold near-complete circular MAGs (cMAGs) with 0% contamination were obtained from Nanopore sequencing data. In conclusion, we have filled a research gap in the genomes and gene catalogues of culturable microbes of sugarcane, providing a vital data resource for further understanding the genetic basis and functions of these microbes. In addition, our methodology and results can provide guidance and reference for other plant microbial genome and gene catalogue studies. [ABSTRACT FROM AUTHOR]

Background and aims: Drought is one of the main causes of global crop decline. Plant growth-promoting rhizobacteria enhance plant tolerance to adverse environmental conditions. This study aimed to determine whether the rhizobacteria Microvirga vignae (BR 3296 and BR 3299) and Bradyrhizobium sp. (BR 3301) can maintain cowpea growth under drought stress. Methods: We analyzed biomass, nodulation, nitrogen accumulation, and physiological traits of the inoculated plants. Rhizobacterial strains were assessed for exopolysaccharide (EPS) and indole acetic acid (IAA) production, growth, and biofilm formation in a water-stress medium induced by polyethylene glycol (PEG)-6000. The expression of genes associated with abscisic acid (ABA) biosynthesis in root nodules was also investigated. Results: All evaluated strains were grown in a culture medium supplemented with PEG. M. vignae strains exhibited increased biofilm formation and EPS production, while Bradyrhizobium showed high IAA production. Cowpea plants inoculated with Bradyrhizobium exhibit higher levels of nodulation, biomass, and nitrogen accumulation. Conversely, M. vignae strains were more efficient at alleviating drought stress and maintaining nodulation, biomass, nitrogen accumulation, and stomatal conductance similar to well-watered plants. Drought-inducible genes were more strongly upregulated in the nodules of plants inoculated with Bradyrhizobium than in those inoculated with M. vignae. Conclusion: Our results suggest that M. vignae strains, isolated from a semi-arid region, help plants withstand water-stress, whereas the strain of Bradyrhizobium sp. isolated from a wet region did not effectively alleviate drought stress. However, Bradyrhizobium sp. conferred growth and nitrogen accumulation to cowpea superior to M. vignae and like plants supplied with nitrogen fertilizer. [ABSTRACT FROM AUTHOR]

Analysis of cyanobacterial diversity is an important step towards identifying new biological resources for production of bioactive compounds. In this study cyanobacterial surface coverage was assessed through satellite image analysis of Tehran drinking water reservoirs in late summer and early autumn of 2018. We also analysed freshwater cyanobacteria including seven local strains purified from surface water samples. Following a polyphasic taxonomic approach combining morphological and molecular methods the culturable strains were classified into Synechococcales and Oscillatoriales, representing at least three families and four genera. Similarity-based analysis of their partial 16S rRNA genes showed 93.4–97.0% sequence identity among the strains from different ecosystems. Considering 95–96% as the overall cut-off for discriminating bacterial species, strains UTMC6011 and UTMC6013 are likely to be new species. Physiological characterization of the new strains and nine others isolated previously by our group from another freshwater ecosystem led to identification of seven nitrogen-fixing, 11 sulphide-tolerant, three salt-tolerant and three heterotrophic strains. Further taxonomic analyses are needed to support investigation of their biotechnological potential. The biodiversity and physiology of cyanobacteria in the main drinking water reservoirs of the megacity, Tehran, were studied by remote sensing and sample analysis. Seven cyanobacterial strains were isolated from the two freshwater lakes. Similarity-based analysis of obtained 16S rRNA gene sequence showed 93.4–97.0% sequence similarity with the strains from other ecosystems. Cyanobacterial isolates of these freshwater reservoirs included seven N2-fixing, 11 sulphide-tolerant, three salt-tolerant and three heterotrophic strains. [ABSTRACT FROM AUTHOR]

Following the latest Permian mass extinction (LPME), abundant unusual sedimentary features and fabrics were widely distributed in Early Triassic carbonate platforms. As a unique type of carbonate grain, spheroids from the Lower Triassic are infrequently reported, yet differ significantly from giant ooids and oncoids. Griesbachian micritic spheroids are well preserved in the Lower Triassic Feixianguan Formation at the Baimiaozi (BMZ) outcrop in Beibei, Chongqing, southwestern China. These spheroids (diameter: 3.9–10.8 mm) were in a marl layer interbedded with massive oolites. They were deposited in the wave troughs of ripple marks comprising micritic clots, sparry calcite, clay minerals, organic matter and pyrite. A microbial spheroid origin is implied based on the coccoidal microbes (coccoid‐like microspherules and bacterial clump‐like microspherules), numerous pyrite framboids (indications suggest the presence of many sulphate‐reducing bacteria and the high iron content in seawater can promote nitrogen‐fixing cyanobacteria proliferation) and microbial‐derived microspherules. The dark‐coloured matrix between the spheroids primarily included microcrystalline calcite, clay minerals, organic matter and metazoan fossils. The spherical and ellipsoidal shapes of the spheroids suggested rapid accretion and lithification. As a unique carbonate depositional mode, Greisbachian spheroids may have been recorded for a palaeo‐ocean with dysoxic and calcium carbonate supersaturation shortly after the LPME. [ABSTRACT FROM AUTHOR]

The discovery of nitrogen fixation in unicellular cyanobacteria provided the first clues for the existence of a circadian clock in prokaryotes. However, recalcitrance to genetic manipulation barred their use as model systems for deciphering the clock function. Here, we explore the circadian clock in the now genetically amenable Cyanothece 51142, a unicellular, nitrogen-fixing cyanobacterium. Unlike non-diazotrophic clock models, Cyanothece 51142 exhibits conspicuous self-sustained rhythms in various discernable phenotypes, offering a platform to directly study the effects of the clock on the physiology of an organism. Deletion of kaiA, an essential clock component in the cyanobacterial system, impacted the regulation of oxygen cycling and hindered nitrogenase activity. Our findings imply a role for the KaiA component of the clock in regulating the intracellular oxygen dynamics in unicellular diazotrophic cyanobacteria and suggest that its addition to the KaiBC clock was likely an adaptive strategy that ensured optimal nitrogen fixation as microbes evolved from an anaerobic to an aerobic atmosphere under nitrogen constraints. The authors investigate the circadian clock in a unicellular diazotrophic cyanobacterium. They demonstrate the role of the clock in regulating intracellular oxygen dynamics, a necessity to accommodate nitrogen fixation in an oxygen-producing cell. [ABSTRACT FROM AUTHOR]

In order to investigate the effects of phosphate solubilizing bacteria and phosphate-solubilizing & nitrogen-fixing bacteria on the content of available selenium (Se) and zinc (Zn) in selenium-rich soil and Camellia sinensis, two strains of endogenous phosphate solubilizing bacteria (Paraburkholderia fungorum PSt07, Kluyvera intermedia PSt12) and two endogenous phosphate-solubilizing & nitrogen-fixation bacteria (Paraburkholderia fungorum PMS05, Kluyvera intermedia PCF06) were used as the research object, and 2 year old tea seedlings of 'Longjing43' and 'Huangjinya' and Se-rich red soil of Kaiyang County, Guizhou Province were used as the test materials. Soil incubation and pot experiment of tea seedlings were carried out. After 60 days of inoculation with each bacterial solution, Se and Zn contents in tea seedlings and available nutrients of nitrogen (N), phosphorus (P), potassium (K), Zn, Se in soil were tested. The results show that the tested strains could increase the content of available P in rhizosphere soil of two tea seedlings, and the content of available N in rhizosphere soil of 'Longjing43'. Under the treatment of phosphate solubilizing bacteria, the content of available Se and Zn in rhizosphere soil and Se in root tissue of 'Longjing43' tea seedlings were increased by 191.83%-573.08%, 37.48%-65.88% and 24.27%-39.73% respectively. The accumulation of Zn in the leaves of the two tea seedlings was increased by 41.23%-247.65% (P<0.05). The contents of available Zn in the rhizosphere soil of potted plants under the treatment of two strains of phosphate solubilizing bacteria were higher than those in the soil incubated with bacteria solution alone without tea plants, indicating that the combined effect of tea plants and phosphate solubilizing bacteria could significantly improve the availability of Zn in soil. The phosphate-solubilizing & nitrogen-fixing bacteria were more beneficial than the phosphate solubilizing bacteria to increase the Se content of 'Huangjinya' root tissue and the available Se content of rhizosphere soil, and PMS05 could significantly increase the content of available Se in rhizosphere soil by 602.00% (P<0.05). The accumulation of Se and Zn elements in tea varied greatly from different combinations of strains and tea cultivars. In practical application, the optimal phosphorus solubilizing strain should be selected for different tea cultivars after completing the strain selection and fertilizer efficiency verification experiment. [ABSTRACT FROM AUTHOR]

Rhizospheric microbes play a crucial role in plant growth promotion. Due to advancements in technology, many nano fertilizers are now applied in the agricultural field. However, its effect on the microbial community is less explored. The present study examines the impact of iron (Fe) nanoparticles (INPs) on paddy rhizospheric (RS) and rhizoplanar (RP) microbes. The effect of different concentrations of INPs iron nanoparticles on the growth of rhizospheric and rhizoplanar microbes was observed by the plate count method. The results showed that bacterial and fungal counts were higher in control than all treatments on 15, 30, and 45 days after sowing seeding (DAS). Nitrogen-fixing bacteria were higher in control on 15 and 30 DAS; however, on 45 DAS, higher nitrogen-fixing bacteria were reported in T4. Phosphate solubilizing microbes were higher in all the treatments compared to the control. Siderophore-producing microbes were higher in control on 15 DAS compared to other treatments. However, after 30 and 45 DAS siderophore-producing microbes were higher in T4 than in control and other treatments. Thus, the results suggest that treatment − 4 (T4) (Seed + Soil +2 g/kg soil) was the best treatment and can be used for plant growth promotion of rice. [ABSTRACT FROM AUTHOR]

Background and aims: Soil salinity negatively affects crop development. Halotolerant nitrogen-fixing bacteria (HNFB) and arbuscular mycorrhizal fungi (AMF) are essential microorganisms that enhance crop nutrient availability and salt tolerance in saline soils. Studying the impact of HNFB on AMF communities and using HNFB in biofertilizers can help in selecting the optimal HNFB-AMF combinations to improve crop productivity in saline soils. Methods: We established three experimental groups comprising apple plants treated with low-nitrogen (0 mg N/kg, N0), normal-nitrogen (200 mg N/kg, N1), and high-nitrogen (300 mg N/kg, N2) fertilizer under salt stress without bacteria (CK, with the addition of 1,500 mL sterile water +2 g sterile diatomite), or with bacteria [BIO, with the addition of 1,500 mL sterile water +2 g mixed bacterial preparation (including Bacillus subtilis HG-15 and Bacillus velezensis JC-K3)]. Results: HNFB inoculation significantly increased microbial biomass and the relative abundance of beta-glucosidase-related genes in the rhizosphere soil under identical nitrogen application levels (p < 0.05). High-nitrogen treatment significantly reduced AMF diversity and the relative abundance of betaglucosidase, acid phosphatase, and urea-related genes. A two-way analysis of variance showed that combined nitrogen application and HNFB treatment could significantly affect soil physicochemical properties and rhizosphere AMF abundance (p < 0.05). Specifically, HNFB application resulted in a significantly higher relative abundance of Glomus-MO-G17-VTX00114 compared to that in the CK group at equal nitrogen levels. Conclusion: The impact of HNFB on the AMF community in apple rhizospheres is influenced by soil nitrogen levels. The study reveals how varying nitrogen levels mediate the relationship between exogenous HNFB, soil properties, and rhizosphere microbes. [ABSTRACT FROM AUTHOR]

This study analyzed the impact of leachate from a temporary landfill on soil microbial diversity in Tingo María, Huánuco region, Peru. Three treatments were used: untreated soil (S), addition of stream water (T0), leachate (T1), and leachate treated by coagulation and flocculation (T2), with 828.5 ml/week added in three weekly doses. Soil samples were collected from the Reserved Forest of the Universidad Nacional Agraria de la Selva. Twenty-one randomly distributed soil samples were taken and homogenized for analysis. Soil quality parameters measured included sand, clay, silt, texture, pH, organic matter, nitrogen, phosphorus and potassium. As for microorganisms, viable aerobes, lactobacilli, actinomycetes, fungi, nitrogen-fixing bacteria, and Escherichia coli were quantified using specific culture and counting methods for each of them. To evaluate the impact of the leachate on microbial diversity, equity indices (Shannon and inverse Simpson), dominance indices (complementary Simpson and Berger Parker) and the percentage composition of each microorganism per treatment were used. An ANOVA was performed to estimate differences in microbial diversity, with a Tukey test at a significance level of α = 0.05. The study showed that leachates affect soil microbial diversity, reducing equity and increasing the dominance of certain species such as E. coli. They also alter physicochemical parameters, decreasing organic matter and nitrogen but increasing other elements such as phosphorus and potassium. This could have implications for soil health and functionality. [ABSTRACT FROM AUTHOR]