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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.

The study was conducted to (i) isolate, select, and identify strains of purple nonsulfur bacteria (PNSB), which can fix nitrogen (N), from soil and water in a rice-shrimp integrated system, (ii) to determine the capacity of the selected potent PNSB strains in producing plant growth promoting substances. The isolation resulted in 57 pure PNSB strains from 36 soil samples and 36 water samples of rice-shrimp paddy fields in Thanh Phu - Ben Tre. Among them, 49 strains survived under pH 5.0 conditions, 24 of which grew well under microaerobic light (ML) and aerobic dark (AD) conditions in a basic isolation medium (BIM) containing NaCl 5‰. Two strains (S01 and S06) with the greatest N fixation were identified by 16S rRNA techniques as Rhodobacter sphaeroides. Their N production was 16.9 mg L-1 under the ML condition and 32.1 mg L-1 under the AD condition. Moreover, two R. sphaeroides S01 and S06 strains performed P solubilization at 0.382-2.954 mg L-1 from Al-P, 3.81-4.28 mg L-1 from Fe-P, and 3.87-4.74 mg L-1 from Ca-P, and production of plant growth promoting substances, such as IAA (12.3-15.5 mg L-1), EPS (1.09-1.58 mg L-1), siderophores (10.7-53.6%) and ALA (1.68-2.82 mg L-1) under both the incubating conditions.

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.

Compost is one of organic fertilizers that play an important role in maintaining soil health and supporting sustainable agriculture. Diverse aspects could be developed to increase the quality of compost. This study aims to compare the quality of compost produced by using two different bioactivators, namely aerobic bioactivator RMC (the microbial consortia isolated from composted rice straw, mahogany bark and cassava peels + additional supplement) and fermentative bioactivator (EM4 + molasses) in the composting of the mainly rice straw-based materials. Composting was conducted using a single factor completely randomized design consisting of five levels as follows: C0 (control, rice straw); C1 (rice straw + bioactivator EM4 + molasses); C2 (rice straw + bioactivator RMC + additional supplement); C3 (rice straw + cow dung + bioactivator RMC + additional supplement); C4 (leaf litter + cow dung + bioactivator RMC + additional supplement, as comparison treatment with no rice straw). Among the treatments of C0, C1 and C2, composting the same rice straw material but different bioactivators, C2 showed the highest compost quality and decomposition rate. Among the other three treatments of C2, C3 and C4 composting different materials but using the same bioactivator, C3 showed the highest compost quality, but the three treatments showed the same high decomposition rate. Based on the characteristics of the compost product, including nutrient content, the treatment C3 produced the highest quality, followed by C4 and then C2. Both bioactivators EM4 + molasses and RMC+ additional supplement tended to increase total bacteria, fungi, nitrogen-fixing bacteria and phosphate-solubilizing microbiota in the compost products compared to the control without bioactivator. A set of aerobic bioactivator RMC plus additional supplement serve as one strategy to accelerate the composting process and to enhance the compost quality.

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.

Although silver nanoparticles (Ag NPs) are widely employed in diverse industries, including agriculture, concerns about their adverse effects on plants at higher concentrations prompt exploration of alternatives, such as Ag/SiO2 NCs. Adding nano SiO2 is anticipated to create a complex with Ag+ ions, potentially decreasing their release into the environment and mitigating toxicity. The potential of Ag/SiO2 NCs as plant growth stimulants remains understudied to date. In this context, the study evaluates the impact of Ag/SiO2 NCs on 30-day-old Z. mays plants compared to Ag NPs at 100 and 200 ppm concentrations and on soil health. Soil health analysis revealed that both Ag NPs and Ag/SiO2 NCs supported the proliferation of P-solubilizing and N-fixing bacteria. Bioaccumulation analysis reveals higher Ag content in plants treated with Ag/SiO2 NCs, attributed to reduced agglomeration. Ag NPs exhibited concentration-dependent toxicity as 200 ppm hindered Z. mays growth, chlorophyll levels and absorption of P, Mg and K, whereas 100 ppm was found to be stimulatory. In stark contrast, Ag/SiO2 NCs demonstrated a remarkable capacity to mitigate Ag toxicity. The beneficial impact of Ag/SiO2 NCs on growth metrics, chlorophyll levels, lipid peroxidation, antioxidant enzyme activity and nutrient absorption was observed at both 100 and 200 ppm. However, it was more pronounced at 100 ppm concentration. This suggests that incorporating SiO2 in NCs may counteract the toxic effects of Ag, possibly through the complexation of Ag+ and a slower release mechanism.

Endosymbiotic bacteria (ESB) have important effects on their hosts, contributing to its growth, reproduction and biological functions. Although the effects of exogenous bacteria on the trap formation of nematode-trapping fungi (NTF) have been revealed, the effects of ESB on NTF remain unknown. In this study, we investigated the species diversity of ESB in the NTF Arthrobotrys musiformis using high-throughput sequencing and culture-dependent approaches, and compared bacterial profiles to assess the effects of strain source and culture media on A. musiformis. PICRUSt2 and FAPROTAX were used to predict bacterial function. Our study revealed that bacterial communities in A. musiformis displayed high diversity and heterogeneity, with Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria as the dominant phyla. The ESB between A. musiformis groups isolated from different habitats and cultured in the same medium were more similar to each other than the other groups isolated from the same habitat but cultured in different media. Function analysis predicted a broad and diverse functional repertoire of ESB in A. musiformis, and unveiled that ESB have the potential to function in five modules of the nitrogen metabolism. We isolated nitrogen-fixing and denitrifying bacteria from the ESB and demonstrated their effects on trap formation of A. musiformis. Among seven bacteria that we tested, three bacterial species Bacillus licheniformis, Achromobacter xylosoxidans and Stenotrophomonas maltophilia were found to be efficient in inducing trap formation. In conclusion, this study revealed extensive ESB diversity within NTF and demonstrated that these bacteria likely play important roles in nitrogen cycling, including nematode trap formation.

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.

This study investigated the interaction between extracellular polymeric substances (EPS) and Pb2+, and the toxic effects of Pb2+ on Klebsiella trevisan. According to the experimental data, Pb2+ mainly inhibited the division and reproduction of Klebsiella trevisan during the logarithmic growth period. In addition, the activity of superoxide dismutase (SOD) and the content of malondialdehyde (MDA) were affected, which indicated that Pb2+ had a strong toxic effect on Klebsiella trevisan and could inhibit cell survival. When the concentration of Pb2+ reached 250 mg/L, the cell membrane damage rate reached as high as 95.7%. Three-dimensional excitation-emission matrix (3D-EEM), synchronous fluorescence and two-dimensional correlation spectroscopy (2D-COS) were selected to analyze the interaction between EPS and Pb2+. The results of 3D-EEM showed that the most important component of EPS was protein-like substance. Further linear fitting of the Stern-Volmer model indicated that the quenching process of Pb2+ and EPS was mainly static quenching. Besides, 2D-COS demonstrated that aromatic proteins in EPS were preferred to tryptophan proteins in binding to Pb2+. The findings of this study are of great significance for revealing the binding interaction between EPS and Pb2+, and proving the toxic effect of Pb2+ on nitrogen-fixing bacteria. It also provides a basis for studying the interaction between EPS and heavy metals by using spectral response.

Abstract Background Root-knot nematodes (RKN) are among the most important root-damaging plant-parasitic nematodes, causing severe crop losses worldwide. The plant rhizosphere and root endosphere contain rich and diverse bacterial communities. However, little is known about how RKN and root bacteria interact to impact parasitism and plant health. Determining the keystone microbial taxa and their functional contributions to plant health and RKN development is important for understanding RKN parasitism and developing efficient biological control strategies in agriculture. Results The analyses of rhizosphere and root endosphere microbiota of plants with and without RKN showed that host species, developmental stage, ecological niche, and nematode parasitism, as well as most of their interactions, contributed significantly to variations in root-associated microbiota. Compared with healthy tomato plants at different developmental stages, significant enrichments of bacteria belonging to Rhizobiales, Betaproteobacteriales, and Rhodobacterales were observed in the endophytic microbiota of nematode-parasitized root samples. Functional pathways related to bacterial pathogenesis and biological nitrogen fixation were significantly enriched in nematode-parasitized plants. In addition, we observed significant enrichments of the nifH gene and NifH protein, the key gene/enzyme involved in biological nitrogen fixation, within nematode-parasitized roots, consistent with a potential functional contribution of nitrogen-fixing bacteria to nematode parasitism. Data from a further assay showed that soil nitrogen amendment could reduce both endophytic nitrogen-fixing bacteria and RKN prevalence and galling in tomato plants. Conclusions Results demonstrated that (1) community variation and assembly of root endophytic microbiota were significantly affected by RKN parasitism; (2) a taxonomic and functional association was found for endophytic nitrogen-fixing bacteria and nematode parasitism; and (3) the change of nitrogen-fixing bacterial communities through the addition of nitrogen fertilizers could affect the occurrence of RKN. Our results provide new insights into interactions among endophytic microbiota, RKN, and plants, contributing to the potential development of novel management strategies against RKN. Video Abstract

Abstract Background Sugarcane growth and yield are complex biological processes influenced by endophytic nitrogen-fixing bacteria, for which the molecular mechanisms involved are largely unknown. In this study, integrated metabolomic and RNA-seq were conducted to investigate the interaction between an endophytic bacterial strain, Burkholderia GXS16, and sugarcane tissue culture seedlings. Results During treatment, the colonization of GXS16 in sugarcane roots were determined, along with the enhanced activities of various antioxidant enzymes. Accordingly, 161, 113, and 37 differentially accumulated metabolites (DAMs) were found in the pairwise comparisons of adjacent stages. In addition, transcriptomic analyses obtained 1,371 (IN-vs-CN), 1,457 (KN-vs-IN), and 365 (LN-vs-KN) differentially expressed genes (DEGs), which were mainly involved in the pathways of glutathione metabolism and carbon metabolism. We then assessed the pattern of metabolite accumulation and gene expression in sugarcane during GXS16 colonization. The results showed that both DAMs and DGEs in the upregulated expression profiles were involved in the flavonoid biosynthesis pathway. Overall, p-coumaroyl-CoA in sugarcane roots transferred into homoeriodictyol chalcone and 5-deoxyleucopelargonidin due to the upregulation of the expression of genes shikimate O-hydroxycinnamoyltransferase (HCT), chalcone synthase (CHS), and phlorizin synthase (PGT1). Conclusions This study provides insights into the gene regulatory mechanisms involved in the interaction between GXS16 and sugarcane roots, which will facilitate future applications of endophytic nitrogen-fixing bacteria to promote crop growth.

【Objective】 Reclaimed soils are usually poor in nutrients and the aim of this paper is to investigate the efficacy of nitrogen-fixing bacteria combined with different nitrogen fertilizations in improving fertility of reclaimed soils. 【Method】 The experiments were conducted in pots filled with soil collected from a subsidized coal mining. The soil was incubated with nitrogen-fixing bacteria combined with different nitrogen fertilizers. In each treatment, we measured carbon and nitrogen in microbial biomass, enzymatic activity, total nitrogen, and ammonium and nitrate nitrogen in the soil. 【Result】 Combining nitrogen-fixing bacteria with ammonium or nitrate nitrogen fertilizer increases carbon and nitrogen in microbial biomass, total dissolved nitrogen, ammonium nitrogen in the soil. Compared with treatment with nitrate and ammonium nitrogen fertilization only, their combination with nitrogen-fixing bacteria increases the activity of catalase, sucrase, protease and urease by 4.96%, 17.85%, 12.53% and 6.12% respectively. Correlation analysis shows a close relationship between soil nutrients, enzymatic activity and carbon and nitrogen in microbial biomass; the activity of sucrase, protease and urease is positively correlated with total nitrogen, total dissolved nitrogen and ammonium nitrogen in the soil (P

Farmers usually apply more chemical fertilizers to enhance the yield of strawberries in soilless culture. Humic substances and biofertilizers are now considered essential nutrient sources in sustainable agriculture. The objective of the greenhouse experiment was to observe the effect of humic and fulvic acid (humic substances), and biofertilizer on root growth, nitrogen (N) and phosphor (P) of the growing media, populations of N-fixing and P-solubilizing bacteria in the root zone, and yield of strawberry grown in the cocopeat-based substrate. The experiment was set up in a randomized block design consisting of seven treatments and four replications. The treatments included humic acid, fulvic acid, and biofertilizer in single or combined applications. All data were subjected to analysis of variance and followed by Duncan's Multiple Range Test with p

Endophytic bacteria, especially those that participate in nitrogen fixation, play critical roles in supplying essential nutrients for legume plant growth. Despite that there have been numerous investigations targeting bacterial microbiomes in legume roots and nodules, little is known about embryonic bacteria that facilitate plant nutrient utilization after seed germination. Here, we collected and investigated endophytic bacterial microbiome in edible pea (Pisum sativum) embryos using five representative cultivars and a pea sprout (shoot of pea [SHP]) control. Twenty-six nitrogen-fixing bacteria (NFB) were isolated from pea embryos, with three strains found in fresh grain pea (FGP) and snow pea (SP) exhibiting the strongest nitrogenase activity of above 85 nmol C2H4/mL/h. Some NFB isolates are also potassium-solubilizing bacteria (KSB) or phosphorus-solubilizing bacteria (PSB) utilizing inorganic and/or organic phosphorus. All 26 NFB showed variable levels (0.41 to 7.10 μg/mL) of indole-3-acetic acid (IAA) secretion. The nutrient-solubilizing NFB identified in our research are potential targets for biofertilizer development. They could be useful in converting nitrogen, potassium, and/or phosphorus into usable forms for the plants. At the microbiome level, high-throughput 16S ribosomal RNA (rRNA) sequencing of 40 bacterial collections from pea embryos generated 4234 operational taxonomic units (OTUs) using 97% identity as the threshold for clustering high-quality effective reads (valid tags). Analysis of OTU annotation results revealed similar species community structures, abundance, and diversity in most samples. Our embryo-derived endophytic bacterial pool provides a microbiome platform for seed dormancy and germination research of edible peas, as well as for digging new biofertilizer resources in general.

Improved agricultural practices and rapid industrialization have led to huge waste generation, and the management of this waste is becoming a global concern. The process of vermicomposting has emerged as a method of choice for converting waste into useful manure, with evidence of increase in crop productivity. During vermicomposting, the collective activities of decomposing microorganisms and earthworms lead to the humification of organic/inorganic waste, thereby generating the final product called vermicompost. Different types of industrial wastes such as waste from paper industries, tanneries, sugar mills, and pulp and textile industries have been effectively converted to vermicompost and successfully used to improve plant growth. The vermicompost thus formed was also demonstrated to increase the production of pharmaceutically important plant secondary metabolites such as withanolides and polyunsaturated fatty acids. Microbial amendment with different bacterial and fungal strains during vermicomposting further proves to be beneficial by increasing nitrogen content, decomposing organic waste, providing aeration, and stabilizing the vermicompost. These microorganisms after passing through the earthworm’s intestine increase in numbers in the vermicast, thus becoming enriched in vermicompost, which is particularly important for their use as biofertilizers. The precise role of different microbial pretreatments in improving the quality of vermicompost generated from industrial and agricultural waste is, however, not completely understood. To fill this gap in knowledge, the present article aims to review published literature to highlight the potential of microbial amendment during vermicomposting for bioremediation of industrial and agricultural waste. Microbial pre-composting followed by vermicomposting emerges as an ecofriendly and economical approach for managing agricultural and industrial waste.

Since Inceptisols, in general, contain low soil organic matter and major plant nutrients, inorganic fertilizers are commonly added during corn cultivation. In order to maintain long-term soil health and fertility, bioferilizer and organic ameliorant application are suggested. The addition of nitrogen (N)-fixing bacteria (NFB) can benefit plant growth through the supply of available nitrogen for plant uptake. Organic ameliorants can enhance soil chemical and biological properties. A field trial had been performed to observe the effect of biofertilizer and organic ameliorant on corn growth, N status in soil and plant, and the yield and wasteof corn. The experiment was designed in a Completely Randomized Block Design that consisted of four treatments and six replications. The treatments were 1.2 kg/ha N-fixing mixed biofertilizer, 2 t/ha organic ameliorant, and mixtures of biofertilizer and ameliorant. Control plants received neither biofertilizer nor ameliorant. The experiment results found that N-fixing biofertilizer and ameliorant increased plant height, fully-developed leaves number, soil reaction and N uptake of corn compared to the control. The total-N content was slightly increased after NFB inoculation with and without amelioration over other treatments. Plots treated with biofertilizer and ameliorant produced a higher grain weight compared to the control treatment. Corn wastes such as empty corn cob and husk weight were increased in plants treated with biofertilizer, ameliorant and a combination of both. This study suggested that the combined application of biofertilizer and ameliorant produced 66% more grain yield and 84 % more cob and husk waste compared to untreated plants.

In rice paddy soil, biological nitrogen fixation is important for sustaining soil nitrogen fertility and rice growth. Anaeromyxobacter and Geobacteriaceae, iron-reducing bacteria belonging to Deltaproteobacteria, are newly discovered nitrogen-fixing bacteria dominant in paddy soils. They utilize acetate, a straw-derived major carbon compound in paddy soil, as a carbon and energy source, and ferric iron compounds as electron acceptors for anaerobic respiration. In our previous paddy field experiments, a significant increase in soil nitrogen-fixing activity was observed after the application of iron powder to straw-returned paddy field soil. In addition, combining iron application with 60–80% of the conventional nitrogen fertilizer rate could maintain rice yields similar to those with the conventional nitrogen fertilization rate. It was thus suggested that iron application to paddy soil increased the amount of nitrogen fixed in the soil by enhancing nitrogen fixation by diazotrophic iron-reducing bacteria. The present study was conducted to directly verify this suggestion by 15N-IRMS analysis combined with 15N-DNA-stable isotope probing of iron-applied and no-iron-applied plot soils in an experimental paddy field. In no-iron-applied native paddy soil, atmospheric 15N2 was incorporated into the soil by biological nitrogen fixation, in which diazotrophic iron-reducing bacteria were the most active drivers of nitrogen fixation. In iron-applied paddy soil, the amount of 15N incorporated into the soil was significantly higher due to enhanced biological nitrogen fixation, especially via diazotrophic iron-reducing bacteria, the most active drivers of nitrogen fixation in the soil. Thus, our previous suggestion was verified. This study provided a novel picture of active nitrogen-fixing microorganisms dominated by diazotrophic iron-reducing bacteria in paddy soil, and directly proved the effectiveness of iron application to enhance their nitrogen fixation and increase the incorporation of atmospheric nitrogen into soil. The enhancement of biological nitrogen fixation in paddy fields by iron application may lead to novel and unique paddy soil management strategies to increase soil nitrogen fertility and ensure rice yields with reduced nitrogen fertilizer input and lower environmental nitrogen burdens.

Biological nitrogen fixation is a key process in the nitrogen cycle and the main source of soil available nitrogen. The number and diversity of nitrogen-fixing bacteria directly reflect the efficiency of soil nitrogen fixation. The alpine wetland on the Qinghai-Tibet Plateau (QTP) is degrading increasingly, with a succession toward alpine meadows. Significant changes in soil physicochemical properties accompany this process. However, it is unclear how does the soil nitrogen-fixing bacteria change during the degradation processes, and what is the relationship between these changes and soil physicochemical properties. In this study, the nifH gene was used as a molecular marker to further investigate the diversity of nitrogen-fixing bacteria at different stages of degradation (none, light, and severe degeneration) in the alpine wetland. The results showed that wetland degradation significantly reduced the diversity, altered the community composition of nitrogen-fixing bacteria, decreased the relative abundance of Proteobacteria, and increased the relative abundance of Actinobacteria. In addition to the dominant phylum, the class, order, family, and genus of nitrogen-fixing bacteria had significant changes in relative abundance. Analysis of Mantel test showed that most soil factors (such as pH, soil water content (SWC), the organic carbon (TOC), total nitrogen (TN), and soil C:P ratio) and abundance had a significant positive correlation. TOC, TN, total phosphorus (TP), soil C:P ratio and Shannon had a significant positive correlation with each other. The RDA ranking further revealed that TOC, SWC, and TN were the main environmental factors influencing the community composition of nitrogen-fixing bacteria. It is found that the degradation of the alpine wetland inhibited the growth of nitrogen-fixing bacteria to a certain extent, leading to the decline of their nitrogen-fixing function.

The present study was conducted to investigate and compare the effect of applying various levels of chemical fertilizers and bioinoculants on the growth and yield of sunflower during the 2017-2018 crop year in Hamedan, Iran. This study was executed as two factorial experiments, as a randomized complete block design in three repetitions. Chemical fertilizers containing nitrogen (N) and phosphorus (P) were used in the first experiment, and nitrogen-fixing (NI) and phosphate-solubilizing (BI) bioinoculants were used in the second experiment. The experimental treatments included applying a urea fertilizer (N0=0, N1=45, N2=90 kg pure nitrogen/ha) and a triple superphosphate (P0=0, P1=40, P2=80 kg pure phosphorus/ha), as well as a nitroxin biofertilizer (NI0=0, NI1=0.5, NI2=1 L/ha) and a biophosphorus (BI0=0, BI1=0.5, BI2=1 L/ha). The results indicated that the highest levels of leaf dry weight, number of seeds per head, head diameter, head weight, seed yield, and the plant's biological yield were obtained for the chemical treatment (N2P2) and biological treatment of (NI2BI2). Group comparisons between the chemical and biological treatments did not show a significant difference for any of the studied characteristics, therefore, the results of this study conclude that the investigated levels of bioinoculants could be appropriate alternatives to chemical fertilizers.

Background and Objectives: Plant Growth-promoting Bacteria (PGPB) can replace the dangerous chemical fertilizers and pesticides. The aim of this study was to isolate the PGPBs for Lycopersicon esculentum plant and to determine the appropriate volume for inoculation. Materials and Methods: Plants samples were collected from tomato fields. Nitrogen fixing-PGPBs were isolated from rhizoplane and rhizosphere. Five isolates were screened based on their growth abilities and examined for PGPB traits including phosphate solubilization, and IAA, ammonia and HCN production. After high cell density cultivation, the cells were separated by centrifugation and freeze dried after resuspension in cryoprotectant. The powders were inoculated into sterile soil with a dose of 106, 107 and 108 CFUs/g. Tomato (Lycopersicon esculentum) seeds were sown in soil and after 42 days the shoot length was measured. Results: Most of the potent PGPBs with high growth capacity were isolated from rhizoplane. Maximum phosphate solubilization was 289.7 µg/ml by NFB12 which isolated from rhizoplane. This strain produced the maximum level of IAA. NFB12 produced ammonia without the ability of production of HCN. This strain enhanced shoot length in dosed dependent manner. Surprisingly, inoculation of soil with 108 CFUs/g dramatically decreased the shoot length by 21%. Based on molecular approach NFB12 was identified as Bacillus megaterium. Conclusion: Isolation of specific PGPBS is recommended for sustainable plant production. Our results showed that NBF12 improves tomato plant growth and its effect on tomato plant growth is does dependent. Maximum growth rate of tomato was observed with 107 CFUs/g soil inoculation of NFB12 while higher inoculation showed negative effect.

Nutmeg is important for national and community revenue mainly in Maluku Province where nutmeg seedlings are grown in low-fertility soil without fertilizer. A greenhouse experiment was performed to evaluate the response of nutmeg seedlings following the application of two different biofertilizer concortia. The experimental design was completely randomized block design, which tested the combination treatments of two rates and the application methods of biofertilizer concortium. The rates of “bacillus biofertilizer” was 0.15 and 0.3%, while the rates of “mixed biofertilizer” was 0.5 and 1.0%. Both biofertilizer were inoculated by foliar spray and soil application. The results verified that at 24 weeks after inoculation, biofertilizers increased the seedling growth traits which included plant height, shoot dry weight, leaf surface area, root number, and root dry weight over the control. Soil application by 1% of “mixed biofertilizer” consists of nitrogen-fixing bacteria and phosphate-solubilizing microbes resulted in better seedlings performance. However, the highest plant height was demonstrated by seedlings treated with 0.3% “bacillus biofertilizer” composed of phosphate solubilizing Bacillus. Biofertilizer inoculation also enhanced soil microbes and leaf surface area but did not change the root-to-shoot ratio of the seedlings. The results showed that biofertilizer inoculation improves the growth of nutmeg seedlings.

Less nutrient availability and drought stress are some serious concerns of agriculture. Both biotic and abiotic stress factors have the potential to limit crop productivity. However, several organic extracts obtained from moringa leaves may induce immunity in plants under nutritional and drought stress for increasing their survival. Additionally, some rhizobacterial strains have the ability to enhance root growth for better nutrient and water uptake in stress conditions. To cover the knowledge gap on the interactive effects of beneficial rhizobacteria and moringa leaf extracts (MLEs), this study was conducted. The aim of this experimental study was to investigate the effectiveness of sole and combined use of rhizobacteria and MLEs against nutritional and drought stress in wheat. Nitrogen-fixing bacteria Pseudomonas aeruginosa (Pa) (108 CFU ml–1) was inoculated to wheat plants with and without foliar-applied MLEs at two different concentrations (MLE 1 = 1:15 v/v and MLE 2 = 1:30 v/v) twice at 25 and 35 days after seed sowing (50 ml per plant) after the establishment of drought stress. Results revealed that Pa + MLE 2 significantly increased fresh weight (FW), dry weight (DW), lengths of roots and shoot and photosynthetic contents of wheat. A significant enhancement in total soluble sugars, total soluble proteins, calcium, potassium, phosphate, and nitrate contents validated the efficacious effect of Pa + MLE 2 over control-treated plants. Significant decrease in sodium, proline, glycine betaine, electrolyte leakage, malondialdehyde, hydrogen peroxide, superoxide dismutase (SOD), and peroxide (POD) concentrations in wheat cultivated under drought stress conditions also represents the imperative role of Pa + MLE 2 over control. In conclusion, Pa + MLE 2 can alleviate nutritional stress and drought effects in wheat. More research in this field is required to proclaim Pa + MLE 2 as the most effective amendment against drought stress in distinct agroecological zones, different soil types, and contrasting wheat cultivars worldwide.

Abstract Background Nitrogen is an essential element for sugarcane growth and development and is generally applied in the form of urea often much more than at recommended rates, causing serious soil degradation, particularly soil acidification, as well as groundwater and air pollution. In spite of the importance of nitrogen for plant growth, fewer reports are available to understand the application and biological role of N2 fixing bacteria to improve N2 nutrition in the sugarcane plant. Results In this study, a total of 350 different bacterial strains were isolated from rhizospheric soil samples of the sugarcane plants. Out of these, 22 isolates were selected based on plant growth promotion traits, biocontrol, and nitrogenase activity. The presence and activity of the nifH gene and the ability of nitrogen-fixation proved that all 22 selected strains have the ability to fix nitrogen. These strains were used to perform 16S rRNA and rpoB genes for their identification. The resulted amplicons were sequenced and phylogenetic analysis was constructed. Among the screened strains for nitrogen fixation, CY5 (Bacillus megaterium) and CA1 (Bacillus mycoides) were the most prominent. These two strains were examined for functional diversity using Biolog phenotyping, which confirmed the consumption of diverse carbon and nitrogen sources and tolerance to low pH and osmotic stress. The inoculated bacterial strains colonized the sugarcane rhizosphere successfully and were mostly located in root and leaf. The expression of the nifH gene in both sugarcane varieties (GT11 and GXB9) inoculated with CY5 and CA1 was confirmed. The gene expression studies showed enhanced expression of genes of various enzymes such as catalase, phenylalanine-ammonia-lyase, superoxide dismutase, chitinase and glucanase in bacterial-inoculated sugarcane plants. Conclusion The results showed that a substantial number of Bacillus isolates have N-fixation and biocontrol property against two sugarcane pathogens Sporisorium scitamineum and Ceratocystis paradoxa. The increased activity of genes controlling free radical metabolism may at least in part accounts for the increased tolerance to pathogens. Nitrogen-fixation was confirmed in sugarcane inoculated with B. megaterium and B. mycoides strains using N-balance and 15N2 isotope dilution in different plant parts of sugarcane. This is the first report of Bacillus mycoides as a nitrogen-fixing rhizobacterium in sugarcane.

Abstract: Sugarcane is an important Brazilian commodity, being usually cultivated in soils with low natural fertility. This study aimed to isolate diazotrophic endophytes from sugarcane tissues and evaluate the morphological and physiological characteristics of their colonies as well as their plant growth-promoting (PGP) traits in select diazotrophic endophytic bacteria. Fifty-six bacterial isolates were identified in the sugarcane tissues, and these isolates presented distinct morphological and physiological traits. A total of thirty-five bacterial isolates were biochemically evaluated. Overall, Bacillus was the dominant genus. Isolates of Methylobacterium spp. and Brevibacillus agri were present only in leaves, while Herbaspirillum seropedicae occurred only in stems. Except to IPA-CF45A, all isolates were nitrogenase positive. All endophytes exhibit production of indol 3-acetic acid. Over 50% of endophytes solubilize phosphate, release N-acyl homoserine lactones, and present the activity of 1-aminocyclopropane-1-carboxylic acid deaminase, catalase, lipase and protease. The network analysis showed that isolates belonged to Burkholderia, Herbaspirillum, and Methylobacterium interact with Bacillus. Bacterial endophytes exhibited distinct morphological, physiological, and PGP traits that are useful for sustainable agriculture, highlighting the isolates IPA-CC33, IPA-CF65, IPA-CC9 and IPA-CF27. Further studies on the effects of these diazotrophic endophytes and their potential for providing microbial inoculants for improving sugarcane fields will provide valuable information to maintain the sustainability and environment quality.

This research was aimed at obtaining varieties of soybean adaptive to acid soils and to obtain Plant Growth-Promoting Rhizobacteria (PGPR) isolates that can improve the agronomic characteristics of soybean and increase the ultisols fertility. This research was conducted in two-stages research on Sampali Village, Percut Sei Tuan sub-District, Deli Serdang District, North Sumatra Province, Indonesia from August 2019 until March 2020. The first stage (adaptive varieties screening) using the non-factorial Randomized Block Design (RBD) with the varieties of Argomulyo, Wilis, Kaba, Dena-1, Devon-1, Dega-1, Demas-1, Burangrang, Detam-1, and Kipas Merah. The second stage (application of PGPR isolates singly and in combinations) using the factorial RBD, the first factor of applicative single and the combination of PGPR isolates, the second factor of adaptive varieties including Detam-1 and Wilis. Data were analyzed with ANOVA and followed by DMRT at P

It has been established that maize/soybean intercropping can improve nitrogen use efficiency. However, few studies have addressed how maize/soybean intercropping affects nitrogen-fixing bacterial diversity and N fixation efficiency of intercropped soybean. In this study, nitrogen-fixing bacterial communities, N fixation efficiency, and their relationships with soil properties under three nitrogen fertilization application rates (N0 0 kg/ha, N1 40 kg/ha, N2 80 kg/ha) were explored through field experiments. Nitrogen fixation and nitrogen-fixing bacteria diversity were assessed using 15N natural abundance, Illumina high-throughput sequencing, and nifH (nitrogen fixation) gene copies quantification in the rhizosphere soil of intercropped soybean. The results showed that nitrogen application rates significantly decreased the nitrogen-fixing bacteria diversity, nitrogen fixation efficiency, and nifH gene copies in the rhizosphere soil. Nitrogen fixation efficiency, nodule number, and dry weight of intercropped soybean were highest in the N0 treatment, and nitrogen fixation was the highest in the N1 treatment. The nitrogen-fixing efficiency in N0, N1, and N2 treatments increased by 69%, 59%, and 42% and the nodule number of soybean was 10%, 22%, and 21%, respectively, compared with monocultures. The soybean nitrogen-fixing bacteria diversity in intercropping under N0 and N1 treatments significantly increased compared with monocultures. There was a significant positive correlation between soil nifH gene copies and N fixation efficiency and a negative correlation with soil available nitrogen. Bradyrhizobium abundance in soybean rhizosphere soil decreased significantly with the increase in nitrogen application rates and was significantly correlated with soil AN (available nitrogen) and pH content in the soybean rhizosphere. These results help us to understand the mechanisms by which nitrogen use efficiency was improved, and nitrogen fertilizer could be reduced in legume/Gramineae intercropping, which is important to improve the sustainability of agricultural production.

Consortium biofertilizer containing Nitrogen (N) Fixing Bacteria and Phosphate (P) Solubilizing Bacteria may substitute inorganic fertilizer in vegetable production. A greenhouse experiment was conducted to evaluate the effect of some combinations and doses of consortium biofertilizer and NPK compound fertilizer on available N and P in the soil, fresh weight of caysim (Brassica chinensis L. var. parachinensis.), and their uptake by caisim shoots after grown in low fertility soil. The experimental design was a randomized block design consisting of seven combinations and doses of consortium biofertilizer and compound fertilizer; and three control treatments. All treatments were repeated three times. The results showed that the combination of the which combination treatment of inorganic fertilizer and biofertilizer had a significant effect on the fresh weight of caysim shoots, available P and N and P uptake after harvesting compared to the biofertilizer treatment alone or without fertilization. Several treatments of combined doses of biofertilizers and NPK compound fertilizer produced the same yield as NPK compound fertilizer alone. The application of 300 kg/ha of compound fertilizer combined with 3,75 L/ha of biofertilizer enabled to increase the yield up to 16% compared to NPK fertilizer alone. This experiment explained that inoculation of biofertilizers can reduce the dose of NPK fertilizer to maintain yield, available P residue in soil and P uptake

Intercropping between sugarcane and soybean is widely used to increase crop yield and promote the sustainable development of the sugarcane industry. However, our understanding of the soil microenvironment in intercropping systems, especially the effect of crop varieties on rhizosphere soil bacterial communities, remains poor. We selected two excellent sugarcane cultivars, Zhongzhe1 (ZZ1) and Zhongzhe9 (ZZ9), from Guangxi and the local soybean variety GUIZAO2 from Guangxi for field interplanting experiments. These two cultivars of sugarcane have good drought resistance. Rhizosphere soil samples were collected from the two intercropping systems to measure physicochemical properties and soil enzyme activities and to extract total soil DNA for high-throughput sequencing. We found that the diversity of the rhizosphere bacterial community was significantly different between the two intercropping systems. Compared with ZZ1, the ZZ9 intercropping system enriched the nitrogen-fixing bacteria, increasing the available nitrogen content by 18% compared with that with ZZ1. In addition, ZZ9 intercropping with soybean formed a more compact rhizosphere environment than ZZ1, thus providing favorable conditions for sugarcane growth. These results provide guidance for the sugarcane industry, especially for the management of sugarcane and soybean intercropping in Guangxi, China.

Abstract The objective of this study was to evaluate the effect of the inoculation with nitrogen-fixing bacteria (NFB) and arbuscular mycorrhizal fungi (AMF) and substrates in the production of Samanea saman (rain tree) seedlings. Three substrates and three inoculation treatments were combined in a randomized block design with six repetitions. The Sewage Sludge substrate favored symbiosis with AMF (promoting twelve times more sporulation), while the Commercial substrate favored symbiosis with NFB (promoting 70% more nodulation). The Sewage Sludge substrate provided the best development of S. saman seedlings, as it promoted higher biomass compared to the Commercial and Standard substrates (14% and 150% respectively). The most significant response to inoculation occurred in the seedlings produced in the Standard substrate, in which the inoculated seedlings had higher biomass than those that received fertilization and those that received neither inoculation nor fertilization (20% and 50% respectively).

The effect of compost combined with phosphate solubilizing bacteria and nitrogen-fixing bacteria on chili plants has been investigated in an experiment using polybag. This research aims to examine the roles of phosphate solubilizing bacteria, nitrogen-fixing bacteria, and compost in increasing the growth and yield of chili plants. This research used a randomized block design with a two-factor factorial design consisting of R0: without Microbes, R1: Nitrogen-Fixing Bacteria (NFB), R2: Phosphate solubilizing bacteria + nitrogen-fixing bacteria (PSB + NFB). The second factor was a dose of organic fertilizer (compost), consisting of 4 dose levels, i.e.: P0: Control (Urea, SP-36, KCl), P1: 15 t ha-1 compost, P2: 20 t ha-1 compost, P3: 25 t ha-1 compost. The research results showed that the use of compost at a dose of 20 t ha-1 added by PSB and NFB significantly increased the growth (number of branches, number of leaves, leaf area, chlorophyll content, plant dry weight) and yield (number of fruits, weight of fruits) of chili plants. The average number of chili fruits increased from 37 fruits per plant to 78 fruits per plant.

Abstract Background The negative consequences of industrial agriculture greatly affect human health and the environment. Debating our dietary requirements and challenging the means of food production are necessary. In the first years of transitioning to agroecological production, crop yields normally decrease. Humic acids and beneficial bacteria used as plant growth promoters can be helpful during this stressful time. Metabolite target identification will aid in increasing plant responses to these agents. Materials We evaluated the metabolite fingerprints of maize and sugarcane seedlings after 5 days of treatment with like-humic acids isolated from vermicompost coupled with a combined Herbaspirillum seropedicae and Gluconacetobacter diazotrophicus application. The hydromethanolic foliar extracts were submitted for 1H nuclear magnetic resonance analysis, and the data were explored using chemometrics procedures. After the preliminary screening, the extracts were analyzed by gas chromatography coupled to time of flight mass spectrometry to identify metabolite targets. Results The biostimulant significantly changed the metabolic fingerprints independent of the plant species. The main proton spectral regions changed by biostimulant use were from 0 to 2.5 ppm and 3.5 to 5 ppm, as revealed by a principal component analysis. The main signals corresponded to amino acid, sugar and organic acid chemical shifts. Aspartic acid was the amino acid present in greatest amounts in both leaf extracts. A significant change occurred in the region normally attributed to (CH n )-protons bound to electron-withdrawing groups, such as carboxyls from mucic, ribonic and saccharic acids derived from sugars and aromatic structures from shikimic acid, 4-hydroxybenzoate and 3,4-dihydroxycinnamic acid. The main organic acids altered by the biostimulant were representatives of the tricarboxylic acid cycle (citric, isocitric, aconitic, malic and fumaric acids). Linoleic and myristic acids, 1-mono palmitin and tocopherol were the major lipid components found at greater levels in the treated leaf extracts. Compounds from the oxidative end products of ascorbic acid metabolism, like threonic, isothreonic and oxalic acids, are putative biomarkers of the biostimulant as are the cyclic polyol identified as quinic acid and trehalose, a disaccharide involved in plant stress responses. Conclusion The biostimulant induced significant changes in the metabolite fingerprints of maize and sugarcane seedlings as revealed by nuclear magnetic resonance. Both primary and secondary metabolisms were affected, and 22 putative biomarkers associated with the biostimulant-treated plant phenotype were identified. This agrees with previous work indicating that the stimulation of primary and secondary metabolisms was partially responsible for biostimulant effects on non-leguminous plants. Moreover, these metabolite targets could be used to genetically manipulate metabolic pathways to aid Poaceae breeding programs in increasing biostimulative responses.

Nitrogen is the most abundant element in the atmosphere, however, most often deficient in agricultural lands. This research was an exploratory to get indigenous non-symbiotic nitrogen-fixing bacteria. Soil samples were collectedfrom rhizosphere of green beans. This study was aimed to determine the bacterial population of the three regions; screening, isolation and selection of free nitrogen-fixing bacteria. Antagonism and pathogenicity tests were performed to observe its potential for a biofertilizer product. The highest number of free nitrogen-fixing bacteria was found from forest soil sample of 2.5x 1011CFU/ml. Screening and isolation process has obtained 10 free nitrogen-fixing isolates. Then was selected into 4 isolates namely SNF4, SNF5, SNF7 and SNF8 according to the ammonia production test qualitatively. When an antagonism activity performed, there was no inhibition zone each other. The pathogenicity test did not show the pathogenic symptom. This study also showed that bacterial isolates obtained significantly affected the germination growth of green beans compared to controls. Possibility, bacteria of this type produced growth hormone for a plant. Strain SNF8 has shown the highest ammonium production then was selected for 16S rRNA identification. Similarity test of genome sequence of strain SNF8 had 99% similarity with Bacillus cereus.

Reference genes, also referred to as housekeeping genes (HKGs), play an important role in gene expression analysis by serving as an internal control. These HKGs are usually involved in basic cellular functions and their expression should remain at relatively constant levels. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) has been used to measure gene expression. Since the normalization of gene expression data depends on baseline expression of HKGs, it is important to identify and verify true HKGs for the qRT-PCR analysis. The goal of this study is to identify and confirm HKGs in Bradyrhizobium diazoefficiens, a nitrogen fixing bacterium which forms a symbiotic relationship with soybean. By revealing such HKGs, the normalization of gene expression would be more robust, reliable, and consistent. Here, we analyzed previous gene expression data for B. diazoefficiens under multiple environmental conditions. As a result, we identified seven constitutively expressed genes among 8453 genes across all conditions. Their fold-change values were within a range of −1.25-fold < x < 1.25-fold. We adopted GeNorm, NormFinder, and comparative ∆Ct methods to rank the seven candidate genes based on their expression stability. To validate these potential HKGs, we measured their expression in various experimental conditions, such as heat, pH, and heavy metal stress. The HKGs that were found in B. diazoefficiens were also applied in closely related species by identifying their homologs.

Sugarcane is an economically important crop that is used for the production of fuel ethanol. Diazotrophic bacteria have been isolated from sugarcane tissues, without causing visible plant anatomical changes or disease symptoms. These bacteria can be beneficial to the plant by promoting root growth and an increase in plant yield. Different rates of Biological Nitrogen Fixation (BNF) were observed in different genotypes. The aim of this work was to conduct a comprehensive molecular and physiological analysis of two model genotypes for contrasting BNF efficiency in order to unravel plant genes that are differentially regulated during a natural association with diazotrophic bacteria. A next-generation sequencing of RNA samples from the genotypes SP70-1143 (high-BNF) and Chunee (low-BNF) was performed. A differential transcriptome analysis showed that several pathways were differentially regulated among the two BNF-contrasting genotypes, including nitrogen metabolism, hormone regulation and bacteria recognition. Physiological analyses, such as nitrogenase and GS activity quantification, bacterial colonization, auxin response and root architecture evaluation, supported the transcriptome expression analyses. The differences observed between the genotypes may explain, at least in part, the differences in BNF contributions. Some of the identified genes might be involved in key regulatory processes for a beneficial association and could be further used as tools for obtaining more efficient BNF genotypes.

Field research was conducted in Poland from 2019–2021 to determine the effect of the bacteria Azospirillumlipoferum Br17 and Azotobacter chroococcum, as well as companion red clover on the total protein content and yield in the grain of spring barley cultivated in a system of organic agriculture. Two factors were examined in the field experiment: I. bacterial formulations: 1—control, 2—nitrogen-fixing bacteria (Azospirillumlipoferum Br17, Azotobacter chroococcum), 3—nitrogen-fixing bacteria (Azospirillumlipoferum Br17, Azotobacter chroococcum) + phosphorus-releasing bacteria (Bacillus megaterium var. phosphaticum, Arthrobacter agilis), and 4—nitrogen-fixing bacteria (Azotobacter chroococcum) + plant growth-promoting rhizobacteria (PGPR) (Bacillus subtilis, Bacillus amyloliquefaciens, Pseudomonas fluorescens); II. companion crop: control without a companion crop, red clover, and red clover + Italian ryegrass. In spring barley grain, the total protein content was determined and the total protein yield was calculated. The obtained study results demonstrated that the growing season conditions significantly affected the total protein content and yield in the spring barley grain. The highest total protein content was recorded in the grain of spring barley following an application of nitrogen-fixing bacteria (Azotobacter chroococcum) combined with PGPR (Bacillus subtilis, Pseudomonas fluorescens) and grown with companion red clover.

Basic knowledge of transcriptional regulation is needed to understand the mechanisms governing biological processes, i.e., nitrogen fixation by Rhizobiales bacteria in symbiosis with leguminous plants. The RhizoBindingSites database is a computer-assisted framework providing motif-gene-associated conserved sequences potentially implicated in transcriptional regulation in nine symbiotic species. A dyad analysis algorithm was used to deduce motifs in the upstream regulatory region of orthologous genes, and only motifs also located in the gene seed promoter with a p-value of 1e-4 were accepted. A genomic scan analysis of the upstoream sequences with these motifs was performed. These predicted binding sites were categorized according to low, medium and high homology between the matrix and the upstream regulatory sequence. On average, 62.7% of the genes had a motif, accounting for 80.44% of the genes per genome, with 19613 matrices (a matrix is a representation of a motif). The RhizoBindingSites database provides motif and gene information, motif conservation in the order Rhizobiales, matrices, motif logos, regulatory networks constructed from theoretical or experimental data, a criterion for selecting motifs and a guide for users. The RhizoBindingSites database is freely available online at rhizobindingsites.ccg.unam.mx.

Maize (Zea mays) is one of the major crops and widely grown in Indonesia. On average, current maize yields are still below its potential. Thus, it needs to increase by good agricultural practices such as applying biofertilizer, which consists of beneficial bacteria. This research was aimed to find out the impact of the bacterial consortium of nitrogen-fixing bacteria (BPN) and phosphate solubilizing bacteria (BPF) on the maize growth. The study was conducted in the greenhouse and arranged in a completely randomized design (CRD) with treatments, i.e.: (1) negative control (no inorganic fertilizer and BPN-BPF); (2) positive control (100% inorganic fertilizer); (3) only BPN-BPF applied (no inorganic fertilizer); (4) 75% inorganic fertilizer + BPN-BPF; and (5) 50% inorganic fertilizer + BPN-BPF. The results revealed that the consortium of nitrogen-fixing bacteria and phosphate solubilizing bacteria significantly improved certain soil chemical properties, such as C-organic, cation exchange capacity (CEC), and the availability of nitrogen and phosphorus in the soil. Besides, the consortium of BPN and BPF also increased the maize growth and total biomass up to 19%. Further, a consortium of BPN and BPF increased the fertilizer efficiency by reducing the dosage of inorganic fertilizer up to 50%.

The present study investigated the physiological and biochemical characteristics of Enterobacter cloacae HG-1 isolated from saline-alkali soil. We further studied the effect of this strain on the salt tolerance of wheat and on the community structure of nitrogen-fixing bacteria in rhizosphere soil. We determined that the investigated strain had high nitrogen fixation activity and produced iron carriers, 1-aminocyclopropane-1-carboxylic acid deaminase, and plant hormones. The metabolites of this strain contained 2,3-butanediol, [R-(R*, R*)], 2-heptanone, and other growth-promoting and antibacterial substances. The strain was also highly salt-tolerant (10% NaCl). After the inoculation of wheat with the HG-1 strain, we recorded increases in root length, plant height, fresh weight, and dry weight of 19.15%, 18.83%, 16.67%, and 17.96%, respectively, compared with uninoculated plants (P < 0.05). Compared with the leaves of uninoculated plants, the proline concentration in the leaves of inoculated plants increased by 12.43% (P < 0.05), the malondialdehyde level decreased by 27.26% (P < 0.05), K+ increased by 20.69%, Ca2+ increased by 57.53% and Na+ decreased by 31.43% (all P

There have been very few studies on the effects of plant competition on the rhizosphere bacterial community. To investigate the impacts of intra- and interspecific plant competition, we analyzed the responses of rhizosphere bacterial communities to plant density as determined by 16S rRNA gene targeted sequencing. We included five weedy plant species growing in field soil in monocultures and mixed cultures at three densities in a greenhouse experiment. The rhizosphere bacterial community of each species changed more with density in a mixture of all five plant species than in monocultures, so intra- and interspecific plant competition had different effects on the bacterial community. For the dominant plant competitor, Centaurea cyanus, neither intra- nor interspecific competition had major effects on the composition of its rhizosphere bacterial communities. In contrast, the bacterial communities of the weakest competitor, Trifolium repens, were affected differently by intra- and interspecific competition. During increasing intraspecific competition T. repens maintained a highly specialized bacterial community dominated by Rhizobium; while during interspecific competition, the relative abundance of Rhizobium declined while other nitrogen fixing and potentially plant growth promoting taxa became more abundant. Contrary to previous observations made for soil microbial communities, the bacterial rhizosphere community of the weakest competitor did not become more similar to that of the dominant species. Thus, the process of competition, as well as the plant species themselves, determined the rhizosphere bacterial community. Our results emphasize the role of plant-plant interactions for rhizosphere bacterial communities. These effects may feedback to affect plant-plant interactions, and this is an important hypothesis for future research.

In this study, the nitrogen-fixing, Gram-negative soil bacteria Rhizobium anhuiense was successfully utilized as the main biocatalyst in a bacteria-based microbial fuel cell (MFC) device. This research investigates the double-chambered, H-type R. anhuiense-based MFC that was operated in modified Norris medium (pH = 7) under ambient conditions using potassium ferricyanide as an electron acceptor in the cathodic compartment. The designed MFC exhibited an open-circuit voltage (OCV) of 635 mV and a power output of 1.07 mW m−2 with its maximum power registered at 245 mV. These values were further enhanced by re-feeding the anode bath with 25 mM glucose, which has been utilized herein as the main carbon source. This substrate addition led to better performance of the constructed MFC with a power output of 2.59 mW m−2 estimated at an operating voltage of 281 mV. The R. anhuiense-based MFC was further developed by improving the charge transfer through the bacterial cell membrane by applying 2-methyl-1,4-naphthoquinone (menadione, MD) as a soluble redox mediator. The MD-mediated MFC device showed better performance, resulting in a slightly higher OCV value of 683 mV and an almost five-fold increase in power density to 4.93 mW cm−2. The influence of different concentrations of MD on the viability of R. anhuiense bacteria was investigated by estimating the optical density at 600 nm (OD600) and comparing the obtained results with the control aliquot. The results show that lower concentrations of MD, ranging from 1 to 10 μM, can be successfully used in an anode compartment in which R. anhuiense bacteria cells remain viable and act as a main biocatalyst for MFC applications.

Transgenic plants may induce shifts in the microbial community composition that in turn alter microbially-mediated nutrient cycling in soil. Studies of how specific microbial groups respond to genetically modified (GM) planting help predict potential impacts upon processes performed by these groups. This study investigated the effect of transgenic high-methionine soybean cv. ZD91 on nitrogen-fixing and ammonia-oxidizing bacterial populations. A difference in nitrogen-fixing or ammonia-oxidizing bacteria community composition was not found, suggesting that cv. ZD91 does not alter the bacterial populations in rhizosphere soil. This study increases our understanding of the potential effect of transgenic soybean on microbial functional groups within soil by suggesting that nitrogen-transforming bacteria may be useful for future investigations on the GM crops impact in the soil ecosystem.

With its premium wood quality and resistance to pests, teak is a valuable tree species remarkably required for timber trading and agroforestry. The nursery stage of teak plantation needs critical care to warrant its long-term productivity. This study aimed to search for beneficial teak rhizosphere microbes and assess their teak-growth-promoting potentials during nursery stock preparation. Three teak rhizosphere/root-associated microbes, including two teak rhizobacteria (a nitrogen-fixing teak root endophyte-Agrobacterium sp. CGC-5 and a teak rhizosphere actinobacterium-Kitasatospora sp. TCM1-050) and an arbuscular mycorrhizal fungus (Claroideoglomus sp. PBT03), were isolated and used in this study. Both teak rhizobacteria could produce in vitro phytohormones (auxins) and catalase. With the pot-scale assessments, applying these rhizosphere microbes in the form of consortia offered better teak-growth-promoting activities than the individual applications, supported by significantly increased teak seedling biomass. Moreover, teak-growth-promoting roles of the arbuscular mycorrhizal fungus were highly dependent upon the support by other teak rhizobacteria. Based on our findings, establishing the synergistic interactions between beneficial rhizosphere microbes and teak roots was a promising sustainable strategy to enhance teak growth and development at the nursery stage and reduce chemical inputs in agroforestry.

Inoculated or coated soybean seeds are often sown in agricultural practice. These treatments play a different role depending on the chemical composition of the preparation. The aim of the field experiment was to demonstrate the effectiveness of the developed coating (chitosan + alginate/PEG) and commercial inoculant (HiStick® Soy) applied alone or in combination to soybean seeds. Uncoated (control) seeds were sown for comparison. The research was carried out in 2018–2020 using the cultivar ‘Mavka’. The experiment was located in Makowisko, Podkarpackie Province, Poland. Coating composition was developed in a laboratory belonging to the Łukasiewicz Research Network—Institute of Biopolymers and Chemical Fibers in Łódź, Poland. The main role of the coating is to protect soybean seeds from low temperatures. HiStick® Soy inoculant contains Bradyrhizobium japonicum bacteria which increase nodulation on the roots. The conducted research demonstrated that sowing only coated seeds was not very effective, because the suitable number of nodules had not developed on soybean roots. The application of the inoculant alone positively affected the assessed traits compared to control, however, plant population was lower than expected. The highest seed yield was obtained after sowing coated seeds in combination with the inoculant (4.32 t·ha−1) and only inoculated seeds (4.23 t·ha−1) compared to control (3.64 t·ha−1). The test of the novel seed-coating agent showed that it had an good effect and efficacy, but only in combination with the inoculation procedure.

Agricultural production systems based on the application of synthetic chemical inputs are changing to more ecological management systems. In this context, rhizosphere microorganisms are considered fundamental to improving soil fertility and providing protection to the host plant. The objective of this study was to perform co-inoculation of Sechium edule (Jacq.) Sw. plants (chayote) with Rhizophagus intraradices and Azospirillum brasilense to reduce Phytophthora capsici damage. The chayote seeds were established in bags, and their inoculation was evaluated alone and in combination with R. intraradices and A. brasilense, in addition to inoculating the stem 14 days after planting with P. capsici. Eight treatments were distributed completely at random, with four repetitions. Morphological and physiological yield variables were recorded at 28, 56, and 84. It was found that S. edule treatment with R. intraradices and A. brasilense increased dry matter allocation in the morphological and physiological performance components. The biomass of plants inoculated with P. capsici and biofertilized with R. intraradices and A. brasilense decreased by 27%, which is relevant, since, under field conditions, plants infected with P. capsici die. Petiole biomass and leaf area decreased during the three evaluation periods with the presence of P. capsici. The other components had a differential response.

The study was performed to evaluate the nutritional value and antioxidant properties of cowpea grain, where plants were grown under conditions of tripartite symbiosis (cowpea plants, nitrogen-fixing bacteria (Bradyrhizobium japonicum) and arbuscular mycorrhizal fungi, (Glomus intraradices) without fertilization. Cowpea plants (Vigna unguiculata (L.) Walp) cv. Hrisi were grown in a glasshouse until the full maturity of grain on the Alluvial meadow soil (Eutric Fluvisol) at three levels of water-holding capacity (40, 60 and 80%). Bradyrhizobium japonicum solely and in combination with arbuscular mycorrhizal fungi increased the content of proteins, soluble sugars and total phenols in the cowpea seeds. When dual inoculation has applied the levels of proteins and soluble sugars in the cowpea grain did not reduce at 40%, nor at 80% in comparison with the optimal water-holding capacity level (60%). Antioxidant capacity at 40% water-holding capacity was determined by the increased content of water soluble antioxidants, flavonoid content and increased ferric reducing power activity and increased antioxidant levels was expressed more distinguished in the treatments with dual inoculation. Slight change of antioxidants in the grain of cowpea was established at an elevated level of water supply. Nutritional value of a grain of cowpea after dual inoculation with Bradyrhizobium strains and Glomus intraradices was not determined by the water-holding capacity levels.

To isolate and characterise free nitrogen-fixing bacteria, we collected randomly soil samples from different areas of Ha Noi. Nitrogen-fixing bacteria were isolated using Burk’s medium without nitrogen mineral supplement. The ammonia (NH4+) synthesis of these bacterial strains after biomass production was determined by means of Nessler reagent. Based on the results of isolation, we observed and evaluated colony and cellular morphology, pigment production, and metabolic activities of twenty-five isolates. Among the isolated bacteria, two bacterial strains (6.2 and 8.2) with high NH4+ concentration in the cultural medium were selected as the best strains for nitrogenfixing ability. The optimal pH and temperature for their growth and nitrogen fixation are 7.0 and 30°C, respectively. Growth is best favored in the presence of sucrose. We sequenced the 16S rRNA gene of selected strains and compared the homology of them in GenBank using BLAST search. The result of the comparison shows that the 6.2 and 8.2 strains have 99% and 100% 16S rRNA-sequence similarity with Pseudomonas sp. and Bacillus sp., respectively.

Plant growth-promoting bacteria (PGPB) and humic acids (HA) have been used as biostimulants in field conditions. The complete genomic and proteomic transcription of Herbaspirillum seropedicae and Gluconacetobacter diazotrophicus is available but interpreting and utilizing this information in the field to increase crop performance is challenging. The identification and characterization of metabolites that are induced by genomic changes may be used to improve plant responses to inoculation. The objective of this study was to describe changes in sugarcane metabolic profile that occur when HA and PGPB are used as biostimulants. Inoculum was applied to soil containing 45-day old sugarcane stalks. One week after inoculation, the methanolic extracts from leaves were obtained and analyzed by gas chromatography coupled to time-of-flight mass spectrometry; a total of 1,880 compounds were observed and 280 were identified in all samples. The application of HA significantly decreased the concentration of 15 metabolites, which generally included amino acids. HA increased the levels of 40 compounds, and these included metabolites linked to the stress response (shikimic, caffeic, hydroxycinnamic acids, putrescine, behenic acid, quinoline xylulose, galactose, lactose proline, oxyproline and valeric acid) and cellular growth (adenine and adenosine derivatives, ribose, ribonic acid and citric acid). Similarly, PGPB enhanced the level of metabolites identified in HA-treated soils; e.g., 48 metabolites were elevated and included amino acids, nucleic acids, organic acids, and lipids. Co-inoculation (HA+PGPB) boosted the level of 110 metabolites with respect to non-inoculated controls; these included amino acids, lipids and nitrogenous compounds. Changes in the metabolic profile induced by HA+PGPB influenced both glucose and pentose pathways and resulted in the accumulation of heptuloses and riboses, which are substrates in the nucleoside biosynthesis and shikimic acid pathways. The mevalonate pathway was also activated, thus increasing phytosterol synthesis. The improvement in cellular metabolism observed with PGPB+HA was compatible with high levels of vitamins. Glucuronate and amino sugars were stimulated in addition to the products and intermediary compounds of tricarboxylic acid metabolism. Lipids and amino acids were the main compounds induced by co-inoculation in addition to antioxidants, stress-related metabolites, and compounds involved in cellular redox. The primary compounds observed in each treatment were identified, and the effect of co-inoculation (HA+PGPB) on metabolite levels was discussed.

Alpine ecosystems are vulnerable to ever-changing environmental conditions, leading to shifts in vegetation distribution and composition with implications on soil functionality and carbon (C) turnover. Although deadwood represents an important global C stock, scarce information is available on how slope exposure influences the wood-inhabiting microbiota throughout the decomposition process in an Alpine setting. We therefore evaluated the impact of slope exposure (north- vs. south-facing sites) on physicochemical and microbiological properties (microbial abundance based on real-time PCR: fungal 18S rRNA, dinitrogen reductase [nifH]; microbial biomass: double strand DNA; and microbial activity: hydrolytic enzyme activities of the main nutrient cycles) of Picea abies wood blocks and the underlying soil in a field experiment in the Italian Alps during a three-year period. Overall, a higher abundance of fungi and nitrogen-fixing bacteria was recorded in the soil at the north-facing site where cooler and moister conditions were observed. In contrast, no exposure effects were found for these two microbial groups in the wood blocks, while their abundance increased over time, accompanied by more acidic conditions with progressing decay. The impact of exposure was also enzyme specific and time dependent for both the P. abies wood blocks and the underlying soil.

The misuse of fertilizers has become a growing concern in terms of agricultural and environmental sustainability. One alternative to reduce the impact of chemical fertilizers is the use of inoculants containing nitrogen-fixing and plant growth promoting bacteria. This study aimed at evaluating the effects of an inoculant with Azospirillum brasilense on the growth and yield of secondharvest maize. The experimental design was randomized blocks with three replications, in a 3 × 5 factorial scheme. The treatments consisted of three inoculation methods (control without inoculation, seed inoculation and leaf-sprayed inoculation at the V4 stage) and five cover N-fertilization doses (0 %, 25 %, 50 %, 75 % and 100 %, with the 100 % dose corresponding to 50 kg ha-1 of N as urea). Inoculated plants showed a greater growth for height (9.5 % and 16 %), stem dry biomass (49 % and 6.75 %) and root dry biomass (123 % and 97 %), respectively for seed inoculation and spraying, as well as increases in ear size (8 %), chlorophyll content (4 %), 1,000-grain weight (12 %) and grain yield (29 %), when compared to non-inoculated plants. The effects of N doses were only significant for 1,000-grain weight and grain yield (kg ha-1), with seed inoculation providing a higher yield for second-harvest maize.

Although Azospirillum strains used in commercial inoculant formulations presents diazotrophic activity, it has been reported that their ability to produce phytohormones plays a pivotal role in plant growth-promotion, leading to a general recommendation of its use in association with regular N-fertilizer doses. In addition, a high variability in the effectiveness of Azospirillum inoculants is still reported under field conditions, contributing to the adoption of the inoculation technology as an additional management practice rather than its use as an alternative practice to the use of chemical inputs in agriculture. To investigate whether the content of stress-resistance biopolymers would improve the viability and performance of Azospirillum inoculants when used as substitute of N-fertilizers, biomass of A. brasilense strain Ab-V5 enriched in exopolysaccharides (EPS) and polyhydroxybutirate (PHB) was produced using a new culture medium developed by factorial mixture design, and the effectiveness of resulting inoculants was evaluated under field conditions. The culture medium formulation extended the log phase of A. brasilense cultures, which presented higher cell counts and increased EPS and PHB contents than observed in the cultures grown in the OAB medium used as control. An inoculation trial with maize conducted under greenhouse conditions and using the biopolymers-enriched Ab-V5 cells demonstrated the importance of EPS and PHB to the long term bacterial viability in soil and to the effectiveness of inoculation. The effectiveness of liquid and peat inoculants prepared with Ab-V5 cells enriched with EPS and PHB was also evaluated under field conditions, using maize as target crop along different seasons, with the inoculants applied directly over seeds or at topdressing under limiting levels of N-fertilization. No additive effect on yield resulted from inoculation under high N fertilizer input, while inoculated plants grown under 80% reduction in N fertilizer showed yields at levels compared to fully fertilized plants, regardless the inoculation method. The presented data highlights the feasibility to partially substitute the N-fertilizer demand in non-legume crops using high-quality inoculant formulations, prepared with diazotrophic bacteria enriched with stress-resistance biopolymers that confer increased viability an effectiveness to the bacterial cells.