Search Results (69)

(1) Background: Improving nitrogen use efficiency in peanuts is essential for achieving a high yield with reduced nitrogen fertilizer input. This study investigates the role of the fungal endophyte Phomopsis liquidambaris in regulating nitrogen utilization throughout the entire growth cycle of peanuts. (2) Methods: Field pot experiments and a two-year plot trial were conducted. The effects of Ph. liquidambaris colonization on the rhizosphere microbial community, soil nitrogen forms, and peanut physiology were analyzed. (3) Results: Colonization by Ph. liquidambaris significantly suppressed the abundance of ammonia-oxidizing archaea (AOA) and bacteria (AOB) in the rhizosphere at the seedling stage. This led to a transient decrease in nitrate and an increase in ammonium availability, which enhanced nodulation-related physiological responses. Concurrently, the peanut-specific rhizobium Bradyrhizobium sp. was enriched in the rhizosphere, and the root exudates induced by the fungus further stimulated nodulation activity. These early-stage effects promoted the establishment of peanut–Bradyrhizobium symbiosis. During the mid-to-late growth stages, the fungus positively reshaped the composition of key functional microbial groups (including diazotrophs, AOA, and AOB), thereby increasing rhizosphere nitrogen availability. (4) Conclusions: Under low nitrogen fertilization, inoculation with Ph. liquidambaris maintained yield stability in long-term monocropped peanuts by enhancing early nodulation and late-stage rhizosphere nitrogen availability. This study provides a promising microbe-based strategy to support sustainable legume production with reduced nitrogen fertilizer application. Full article

Traditional clean tillage in peach orchards leads to soil degradation and nitrogen (N) loss. While inter-row grassing can optimize N cycling, the specific rhizosphere microbial mechanisms involved have not been fully understood. This study investigated how different inter-row grassing modes influence N availability through microbial communities in a peach orchard. The experiment included a monoculture of Trifolium repens L. (Tr), a monoculture of Lolium perenne L. (Pr), their mixture (TPr), and clean tillage (CK). By combining soil physicochemical analyses, metagenomic sequencing, functional gene quantification, and multivariate statistics, the study systematically examined the impacts of inter-row grassing modes on soil N cycling. The results showed that inter-row grassing modes played a significant role in reshaping N processes. Pr enhanced mineralization and nitrification, increasing inorganic N through specific genes (amoA, hao). Tr, on the other hand, promoted diazotrophs (Bradyrhizobium) and dissimilatory nitrate-reducing bacteria, enhancing biological N fixation and retention. TPr combined these benefits, leading to enhanced nitrification, increased labile carbon, and elevated enzyme activities, creating a complex microbe–gene network that mediated nitrification and denitrification. Overall, inter-row grassing modulates rhizosphere functions by enhancing N cycling through a “carbon input–microbial regulation” mechanism, offering an effective strategy for improving N use efficiency and promoting sustainable orchard management. Full article

As a pulse crop, mung beans are associated with nitrogen-fixing bacteria, which can improve soil fertility, lower the need for nitrogen fertilizers, and increase yield and soil quality for subsequent harvests. This study aimed to identify effective rhizobial inoculants for mung beans (Vigna radiata L.) by evaluating selected strains for cowpea (Vigna unguiculata L.), soybean (Glycine max L.), and common bean (Phaseolus vulgaris L.) under controlled (axenic) conditions. Cowpea, soybean, and common bean strains were tested as mung beans inoculants under axenic conditions. Promising strains were then tested in the field to assess grain yield and to quantify nitrogen fixation using the ¹⁵N natural abundance method. The cowpea strain BR 3302 (Bradyrhizobium viridifuturi) increased mung bean yield by 18%, achieving results similar to a 240 kg N ha⁻¹ fertilizer application. The soybean strain BR 96 (B. elkanii) facilitated the highest nitrogen fixation (35.3 kg N ha⁻¹), significantly surpassing the contribution of indigenous diazotrophic bacteria (18.5 kg N ha⁻¹). Interestingly, BR 3302 appeared to primarily enhance nitrogen uptake from the soil (65% of plant N), indicating the presence of other potential plant growth-promoting mechanisms beyond nitrogen fixation. This research demonstrates that Bradyrhizobium strains can benefit mung beans through both enhanced nitrogen fixation and additional growth-promoting mechanisms, offering a sustainable approach to improve mung beans production. Full article

Improving nitrogen use efficiency (NUE) in maize is critical for reducing fertilizer inputs and mitigating environmental impacts. The rhizosphere microbiome—the plant’s “second genome”—plays a key role in nitrogen acquisition, assimilation, and signaling. This review synthesizes recent advances from multi-omics studies, functional validation, and field experiments, highlighting how maize roots recruit and coordinate microbial taxa, including diazotrophs, nitrifiers, organic nitrogen mineralizers, and growth-promoting bacteria, to enhance NUE under variable nitrogen availability. We integrate mechanistic insights into transporter-mediated nitrogen uptake, microbial regulation of root development and exudation, and host genetic determinants, such as ZmC2, ZmSBT3, and ZmNLP8, that influence microbiome assembly. Evidence from synthetic communities, isotope tracing, and host–microbiome association studies demonstrates that microbial contributions to plant nitrogen can be substantial and genetically modulated. Finally, we discuss microbiome-based interventions, including functional strain discovery, microbial fertilizers, biostimulants, and microbiome-assisted breeding, assessing their potential and limitations. We conclude by highlighting key challenges and proposing an integrative framework to guide microbiome-informed strategies for sustainable improvement of maize NUE. Full article

Saline and highly alkaline soda lakes are often characterized by a persistent nitrogen loss and high sulfide levels. Cyanobacteria are key aerobic diazotrophs in soda lakes, where light-dependent nitrogen fixation (NF) is crucial for sustaining ecosystem functioning. While sulfide is a well-known inhibitor of oxygenic photosynthesis, some cyanobacteria may tolerate it and utilize it via anoxygenic photosynthesis. In this study, we investigated the NF and anoxygenic photosynthesis in the genus Sodalinema, including non-heterocystous cyanobacteria widely distributed in soda and saline environments around the world and possessing an anaerobe-like nitrogenase. Our data suggest that their nif-operon could have been more likely acquired in soda or saline–alkaline lakes from natronophilic sulfate-reducing bacteria of the family Desulfonatronovibrionaceae than in the marine environment. It was shown that Sodalinema sp. P-1104, isolated from a southwestern Siberian soda lake, is capable of NF only in a light/dark switching mode, both in oxic and anoxic conditions. Sulfide did not suppress photosynthesis and stimulated NF up to threefold in oxygenic conditions. Anaerobic NF was obligately sulfide-dependent and supported by anoxygenic photosynthesis. However, removal of photosynthetic oxygen due to the high reducing potential of sulfide stimulated NF to a greater extent than does the use of sulfide through anoxygenic photosynthesis. Full article

Peat mosses of the genus Sphagnum are keystone species in peatland ecosystems and play critical roles in carbon sequestration, nitrogen fixation, and hydrological regulation. Indeed, these ecological functions are largely mediated by endophytic bacteria associated with Sphagnum. Here, five populations of the endemic Chinese moss species, S. multifibrosum, were sampled across southern China in peatland (PH) and rock habitats (RH). High-throughput sequencing of 16S rRNA and nitrogenase (nifH) genes was applied to characterize overall endophytic bacterial diversity and diazotroph diversity associated with S. multifibrosum, respectively, alongside host microsatellite genotyping. Proteobacteria was the dominant endophytic bacterial phylum. The bacterial communities exhibited significant spatial separation between eastern and western communities and community dissimilarities significantly increased with increasing geographic distances. Environmental heterogeneity and host genetics jointly shaped endophytic bacterial community assemblage. Climate was the most important determinant influencing bacterial composition, followed by host genotype and habitat type. Temperature, precipitation, and nitrogen deposition were the primary environmental factors that influenced composition. Bacterial diversity and composition exhibited no statistically significant differences between the two habitats. Further, the richness and abundances of diazotrophs and methanotrophs from PH communities were higher than in RH communities. Co-occurrence network analysis suggested that RH bacterial networks had lower connectance but were more modularized and exhibited higher complexity than PH networks. These results highlight the ecological functions of peat mosses in carbon and nitrogen cycling and suggest a need to prioritize the conservation of S. multifibrosum in peatland environments under global climate change. The results also provide a framework to help future wetland management and biodiversity conservation efforts in China. Full article

Biosurfactants (BS) are surface-active compounds synthesized by microorganisms with broad industrial applications. Although BS-producing strains are widely reported, little is known about their production by diazotrophic bacteria. This study investigated, for the first time, the BS produced by Bradyrhizobium sp. ESA 81, a diazotrophic bacterium isolated from the Brazilian semiarid region. The strain was cultivated in the mineral medium using sunflower oil and ammonium nitrate as carbon and nitrogen sources. The compound was chemically characterized using TLC, FAME, FTIR, and mass spectrometry (MALDI-TOF). The results revealed a mixture of glycolipids composed of trehalose linked to fatty acid chains ranging from C9 to C18. The BS exhibited a surface tension of 31.8 mN/m, a critical micelle concentration of 61.2 mg/L, and an interfacial tension of 22.1 mN/m. The BS also showed an emulsification index (EI24) of 55.0%. High stability was observed under extreme conditions of temperature (−20 to 121 °C), pH (2–12), NaCl (5–20%), and sucrose (1–5%). These findings indicate that the trehalolipid BS produced by Bradyrhizobium sp. ESA 81 is a stable and efficient surface-active agent, with promising potential for use in biotechnological and industrial processes. Full article

Phyllosphere microbial communities influence the growth and productivity of plants, particularly in epiphytic plants, which are disconnected from nutrients available in the soil. We characterized the phyllosphere of 30 individuals of the epiphytic cycad, Zamia pseudoparasitica, collected from three forest sites during the rainy and dry seasons in the Republic of Panama. We used DNA metabarcoding to describe the total bacteria community with the 16S rRNA gene and the diazotrophic community with nifH gene. Common taxa included members of the Rhizobiales, Frankiales, Pseudonocardiales, Acetobacteriales, and the diazotrophic community was dominated by Cyanobacateria. We observed similar patterns of alpha diversity across sites and seasons, and no community differences were seen within sites between the rainy and dry seasons for either the 16S rRNA or nifH genes. However, pairwise comparisons showed some statistically significant differences in community composition between sites and seasons, but these explained only a small portion of the variation. Beta diversity partitioning indicated that communities were more phylogenetically closely related than expected by chance, indicative of strong environmental or host filtering shaping these phyllosphere communities. These results highlight the influence of host-driven selection and habitat stability in shaping phyllosphere microbiota, offering new insights into microbial assembly in tropical canopy ecosystems. Full article

Zinc deficiency is a major contributor to hidden hunger, affecting billions of people worldwide, particularly in vulnerable populations. Agronomic biofortification with zinc is a promising strategy to increase both crop productivity and the nutritional quality of food, especially in countries like Brazil, where tropical soils are often deficient in this micronutrient. This review analyzes the main technologies applied in the zinc biofortification of edible crops in Brazil, including fertilizer types, application methods, doses, and the use of innovative approaches such as nano-fertilizers and biofertilizers. The results show that the foliar application of zinc sulfate at doses of 600 g ha⁻¹ increased zinc concentration in grains by 25–40% without reducing crop yields. Additionally, the use of zinc nanoparticles increased wheat grain zinc content by up to 30% and biomass production, while biofertilizer application with diazotrophic bacteria raised zinc concentration in maize grains by 12.7–18.2%. These technologies demonstrate potential for enhancing zinc use efficiency and improving the nutritional quality of crops. Standardizing biofortification practices is essential to maximize their impact on food and nutritional security, contributing to the prevention of zinc deficiency in human populations. Full article

Residue incorporation is a universally accepted agronomic practice around the world. However, the relationship between C and N turnover in soil is still not fully understood. We performed a soil microcosm incubation experiment to study the effects of residue incorporation with different C-to-N ratios (C/N) (low, 31.8; high, 84.5) on the SOC distribution, diazotrophic bacterial composition, and N accumulation in different particle size fractions (PSFs) of three types of soil parent material with different native C/N ratios. Our results demonstrate that SOC is 1.34 to 2.50 times more easily retained and accumulated in clay compared to baseline levels at the early stage of soil development. The native C/N ratio markedly affects the microbial metabolic characteristics and the SOC accumulation processes. Specifically, low C/N residue enhanced SOC accumulation in high-native-C/N soil, while the high-C/N residue maximized SOC in low-native-C/N soil. These shifts regulated the composition of the diazotrophic bacterial community, increasing the nitrogenase coding gene (nifH) abundance 5.57- and 8.1-fold in low-C/N residue treatments and 6.6-fold in the high-C/N residue treatment, thereby promoting soil N accumulation. Moreover, we highlight the potential role of Bradyrhizobiaceae, Rhodospirillaceae, Micrococcaceae, Rhizobiaceae, Comamonadaceae, Nitrospiraceae, and Burkholderiaceae in biological N fixation during pedogenesis. This study explored the coupling relationship between soil native and residue C/N and soil biological N fixation at the soil particle level, and the results suggest that residue incorporation to improve soil fertility needs to be further explored according to soil native C/N. Full article

Nitrogen is an essential plant nutrient, but N fertilization contributes to greenhouse gas emissions through its production and application as well as nitrous oxide emissions when applied to soil. Diazotrophic bacteria, known to modify root architecture and increase nutrient uptake, have been proposed as a potential strategy to improve nitrogen use efficiency (NUE) in sugarcane cultivation. The objective of this study was to evaluate the efficiency of N use from ¹⁵N ammonium sulfate applied to different sugarcane varieties inoculated with diazotrophic bacteria. The experiment was conducted in pots filled with soil (100 kg pot⁻¹). The sugarcane varieties tested were RB867515 and RB92579. A commercial diazotrophic bacteria inoculant for sugarcane was used. The experimental design was a randomized block design with four replicates. The treatments were as follows: control without inoculation, inoculation with five strains of bacteria, with or without nitrogen fertilization. The evaluations were performed on different parts of the plant. At 360 days after transplanting, the accumulation of N, fresh mass, dry mass, and the proportion of excess ¹⁵N were determined. In the studied sugarcane varieties, the efficiency of ¹⁵N fertilizer use was 60%, with no influence from inoculation. Full article

Two novel marine hydrogen- and sulfur-oxidizing bacteria, designated HSL1-7^T and HSL3-1^T, were isolated from mangrove sediments from Fujian Province, China. Strain HSL1-7^T exhibited Gram-negative, rod-shaped to slightly curved morphology with polar flagellum-driven motility, whereas strain HSL3-1^T was Gram-negative, rod-shaped and non-motile. Strain HSL1-7^T and HSL3-1^T were obligate chemolithoautotrophs, capable of using molecular hydrogen and thiosulfate as an energy source, and molecular oxygen and elemental sulfur as the electron acceptors for growth. Cellular fatty acid profiles revealed similar predominant components (C_16:1ω7c, C_16:0, C_18:1ω7c, and C_14:0) in both strains. Strains HSL1-7^T and HSL3-1^T were strongly diazotrophic, as demonstrated by ¹⁵N₂ fixation when a fixed nitrogen source was absent from the growth medium. The DNA G+C contents of strains HSL1-7^T and HSL3-1^T were determined to be 36.1% and 57.3%, respectively. Based on the 16S rRNA gene sequences, strains HSL1-7^T and HSL3-1^T exhibited the highest sequence similarities with Sulfurimonas marina B2^T (98.5% and 94.45%, respectively). Notably, the 16S rRNA gene sequence similarity between strains HSL1-7^T and HSL3-1^T was 93.19%, indicating that they represent distinct species within the genus Sulfurimonas. Comparative genomic analyses revealed the presence of diverse metabolic profiles in strains HSL1-7^T and HSL3-1^T, including carbon fixation, hydrogen oxidation, sulfur oxidation, and nitrogen fixation. The combined phenotypic, chemotaxonomic, and phylogenetic evidence, including average nucleotide identity and in silico DNA-DNA hybridization values, shows that strains HSL1-7^T and HSL3-1^T represent two novel species of the genus Sulfurimonas for which the names Sulfurimonas microaerophilic sp. nov. and Sulfurimonas diazotrophicus sp. nov. are proposed, with the type strains HSL1-7^T (=MCCC 1A18899^T = KCTC 25640^T) and HSL3-1^T (=MCCC 1A18844^T), respectively. Full article

The development of microbial-based biostimulants to enhance the growth of crops and support a healthy and sustainable soil requires the isolation and large-scale industrial culture of effective microorganisms. In this study, work was undertaken to isolate and characterize free-living nitrogen-fixing bacteria capable of acting as biostimulants alone or by incorporation into and/or supplementation with a current commercial crop biostimulant for farmers. Free-living bacteria were isolated from soil, sugar cane mulch, and plant roots following preliminary culture in a nitrogen-free media that targeted specific groups of known diazotrophs. Following the identification of each isolate by 16S rDNA sequence analysis, isolates selected for further study were identified as most closely related to Priestia megaterium, Sphingobium yanoikuyae, and Burkholderia paludis. Each isolate was investigated for its capacity to promote plant growth in nitrogen-free media. Wheat seedlings were inoculated with the isolates separately, together as a consortium, or in combination with the commercial biostimulant, Great Land Plus^®. Compared to no-treatment control plants, the fresh weights were higher in both the shoots (183.2 mg vs. 330.6 mg; p < 0.05) and roots (320.4 mg vs. 731.3 mg; p < 0.05) of wheat seedlings inoculated with P. megaterium. The fresh weights were also higher in the shoots (267.8 mg; p < 0.05) and roots (610.3 mg; p = 0.05) of wheat seedlings inoculated with S. yanoikuyae. In contrast, the fresh weight of the shoot and root systems of plants inoculated with B. paludis were significantly lower (p < 0.05) than that of the no-treatment control plants. Moreover, when Great Land Plus^® was supplemented with a consortium of P. megaterium and S. yanoikuyae, or a consortium of P. megaterium, S. yanoikuyae, and B. paludis no promotion of plant growth was observed. Full article

Nitrogen inputs for sustainable crop production for a growing population require the enhancement of biological nitrogen fixation. Efforts to increase biological nitrogen fixation include bioprospecting for more effective nitrogen-fixing bacteria. As bacterial nitrogenases are extremely sensitive to oxygen, most primary isolation methods rely on the use of semisolid agar or broth to limit oxygen exposure. Without physical separation, only the most competitive strains are obtained. The distance between strains provided by plating on solid media in reduced oxygen environments has been found to increase the diversity of culturable potential diazotrophic bacteria. To obtain diverse nitrogen-fixing isolates from natural grasslands, we plated soil suspensions from 27 samples onto solid nitrogen-free agar and incubated them under atmospheric and oxygen-reducing conditions. Putative nitrogen fixers were confirmed by subculturing in liquid nitrogen-free media and PCR amplification of the nifH genes. Streaking of the 432 isolates on nitrogen-rich R2A revealed many cocultures. In most cases, only one community member then grew on NFA, indicating the coexistence of nonfixers in coculture with fixers when growing under nitrogen-limited conditions. To exclude isolates able to scavenge residual nitrogen, such as that from vitamins, we used a stringent nitrogen-free medium containing only 6.42 μmol/L total nitrogen and recultured them in a nitrogen-depleted atmosphere. Surprisingly, PCR amplification of nifH using various primer pairs yielded amplicons from only 17% of the 442 isolates. The majority of the nifH PCR-negative isolates were Bacillus and Streptomyces. It is unclear whether these isolates have highly effective uptake systems or nitrogen reduction systems that are not closely aligned with known nitrogenase families. We advise caution in determining the nitrogen fixation ability of plants from growth on nitrogen-free media, even where the total nitrogen is very limited. Full article

Microbes such as bacteria and fungi play important roles in nutrient cycling in soils, often leading to the bioavailability of metabolically important mineral elements such as nitrogen (N), phosphorus (P), iron (Fe), and zinc (Zn). Examples of microbes with beneficial traits for plant growth promotion include mycorrhizal fungi, associative diazotrophs, and the N₂-fixing rhizobia belonging to the α, β and γ class of Proteobacteria. Mycorrhizal fungi generally contribute to increasing the surface area of soil-root interface for optimum nutrient uptake by plants. However, when transformed into bacteroids inside root nodules, rhizobia also convert N₂ gas in air into ammonia for use by the bacteria and their host plant. Thus, nodulated legumes can meet a high proportion of their N requirements from N₂ fixation. The percentage of legume N derived from atmospheric N₂ fixation varies with crop species and genotype, with reported values ranging from 50–97%, 24–67%, 66–86% 27–92%, 50–92%, and 40–75% for soybean (Gycine max), groundnut (Arachis hypogea), mung bean (Vigna radiata), pigeon pea (Cajanus cajan), cowpea (Vigna unguiculata), and Kersting’s groundnut (Macrotyloma geocarpum), respectively. This suggests that N₂-fixing legumes require little or no N fertilizer for growth and grain yield when grown under field conditions. Even cereals and other species obtain a substantial proportion of their N nutrition from associative and endophytic N₂-fixing bacteria. For example, about 12–33% of maize N requirement can be obtained from their association with Pseudomonas, Hebaspirillum, Azospirillum, and Brevundioronas, while cucumber can obtain 12.9–20.9% from its interaction with Paenebacillus beijingensis BJ-18. Exploiting the plant growth-promoting traits of soil microbes for increased crop productivity without any negative impact on the environment is the basis of green agriculture which is done through the use of biofertilizers. Either alone or in combination with other synergistic rhizobacteria, rhizobia and arbuscular mycorrhizal (AM) fungi have been widely used in agriculture, often increasing crop yields but with occasional failures due to the use of poor-quality inoculants, and wrong application techniques. This review explores the literature regarding the plant growth-promoting traits of soil microbes, and also highlights the bottle-necks in tapping this potential for sustainable agriculture. Full article