Search Results (539)

Azospirillum is a well-studied genus of plant growth-promoting rhizobacteria (PGPR) and one of the most extensively researched diazotrophs. This genus can colonize rhizosphere soil and enhance plant growth and productivity by supplying essential nutrients to the host. Azospirillum–plant interactions involve multiple mechanisms, including nitrogen fixation, the production of phytohormones (auxins, cytokinins, indole acetic acid (IAA), and gibberellins), plant growth regulators, siderophore production, phosphate solubilization, and the synthesis of various bioactive molecules, such as flavonoids, hydrogen cyanide (HCN), and catalase. Thus, Azospirillum is involved in plant growth and development. The genus Azospirillum also enhances membrane activity by modifying the composition of membrane phospholipids and fatty acids, thereby ensuring membrane fluidity under water deficiency. It promotes the development of adventitious root systems, increases mineral and water uptake, mitigates environmental stressors (both biotic and abiotic), and exhibits antipathogenic activity. Biological nitrogen fixation (BNF) is the primary mechanism of Azospirillum, which is governed by structural nif genes present in all diazotrophic species. Globally, Azospirillum spp. are widely used as inoculants for commercial crop production. It is considered a non-pathogenic bacterium that can be utilized as a biofertilizer for a variety of crops, particularly cereals and grasses such as rice and wheat, which are economically significant for agriculture. Furthermore, Azospirillum spp. influence gene expression pathways in plants, enhancing their resistance to biotic and abiotic stressors. Advances in genomics and transcriptomics have provided new insights into plant-microbe interactions. This review explored the molecular mechanisms underlying the role of Azospirillum spp. in plant growth. Additionally, BNF phytohormone synthesis, root architecture modification for nutrient uptake and stress tolerance, and immobilization for enhanced crop production are also important. A deeper understanding of the molecular basis of Azospirillum in biofertilizer and biostimulant development, as well as genetically engineered and immobilized strains for improved phosphate solubilization and nitrogen fixation, will contribute to sustainable agricultural practices and help to meet global food security demands. Full article

Phosphorus-solubilizing fungi represent a viable alternative to traditional fertilizers for use in coffee cultivation. The aim of this work was to select fungal consortia with a high phosphorus-solubilizing capacity for application to three varieties of coffee plants under greenhouse conditions. The research comprised three phases: Firstly, solubilizing strains were identified morphologically and molecularly. Secondly, compatibility tests were carried out to select combinations of phosphorus-solubilizing fungi. The selection of the consortia was evaluated based on their phosphorus-solubilizing capacity, and the consortia with the solubilizing activity were chosen for application to coffee plants. In the greenhouse phase, three coffee varieties were inoculated; the treatments involved single, dual, and triple inoculation, as well as a control without fungi. Five species were identified: Fusarium crassum, F. irregulare, Leptobacillium leptobactrum, Penicillium brevicompactum, and Trichoderma spirale, plus one strain of Absidia sp. The in vitro phase of the study revealed that 11 consortia demonstrated compatibility, and their phosphorus solubilization capacity and phosphatase activity were evaluated. As a result, four consortia with high phosphorus solubilization capacity were selected for inoculation on coffee plants. The greenhouse phase results showed that the three coffee varieties inoculated in consortia showed higher phosphorus availability in the substrate and significant growth. Full article

Heavy metal contamination in paddy fields poses serious risks to food safety and crop productivity. This study evaluated the potential of native soil fungi as bioinoculants to reduce metal uptake in rice cultivated under contaminated conditions. Eight fungal strains—four indigenous and four allochthonous—were selected based on their plant growth-promoting traits, including siderophore production and phosphate solubilization. Additional metabolic analysis confirmed the production of bioactive secondary metabolites. In a greenhouse experiment, three rice cultivars were grown under permanent flooding (PF) and alternate wetting and drying (AWD) in soil enriched with arsenic, cadmium, chromium, and copper. Inoculation with indigenous fungi under AWD significantly reduced the arsenic accumulation in rice shoots by up to 75%. While AWD increased cadmium uptake across all cultivars, fungal inoculation led to a moderate reduction in cadmium accumulation—ranging from 15% to 25%—in some varieties. These effects were not observed under PF conditions. The results demonstrate the potential of native fungi as a nature-based solution to mitigate heavy metal stress in rice cultivation, supporting both environmental remediation and sustainable agriculture. Full article

Peach fruit flesh spongy tissue disorder causes dry, porous, and brown areas in the flesh, severely compromising fruit quality and market value. While soil properties and calcium nutrition have been linked to the disorder, the role of rhizosphere microbial communities in disorder resistance remains unclear. This study investigated both the physicochemical properties and the root-associated microbiomes of disordered (CK) and healthy (TT) peach orchards to explore microbial mechanisms underlying disorder suppression. TT soils exhibited higher pH, greater organic matter, increased exchangeable calcium, and more balanced trace elements compared to CK. Microbial analysis revealed significantly higher diversity and enrichment of beneficial taxa in TT associated with plant growth and disorder resistance. Functional gene prediction showed TT was enriched in siderophore production, auxin biosynthesis, phosphate solubilization, and acetoin–butanediol synthesis pathways. Co-occurrence network analysis demonstrated that TT harbored a more complex and cooperative microbial community structure, with 274 nodes and 6013 links. Metagenomic binning recovered high-quality MAGs encoding diverse resistance and growth-promoting traits, emphasizing the ecological roles of Gemmatimonadaceae, Reyranella, Nitrospira, Bacillus megaterium, and Bryobacteraceae. These findings highlight the combined importance of soil chemistry and microbiome structure in disorder suppression and provide a foundation for microbiome-informed soil management to enhance fruit quality and promote sustainable orchard practices. Full article

With the increasing severity of global climate change and soil salinization, the development of microorganisms that enhance crop salt tolerance has become a critical focus of agricultural research. In this study, we explored the potential of a novel Streptomyces species Qhu-G9 as a plant growth-promoting rhizobacterium (PGPR) under salt stress conditions, employing whole-genome sequencing and functional annotation. The genomic analysis revealed that Qhu-G9 harbors various genes related to plant growth promotion, including those involved in phosphate solubilization, indole-3-acetic acid (IAA) biosynthesis, antioxidant activity, and nitrogen fixation. A total of 8528 coding genes were annotated in Qhu-G9, with a significant proportion related to cell metabolism, catalytic activity, and membrane transport, suggesting its broad growth-promoting potential. In vitro experiments demonstrated that Qhu-G9 exhibited strong iron siderophore production, IAA synthesis, phosphate solubilization, and 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, all of which correlate with its plant growth-promoting capacity. Further plant growth trials revealed that Qhu-G9 significantly enhances the growth of Avena sativa and Onobrychis viciifolia seedlings under salt stress conditions, improving key physiological parameters, such as chlorophyll content, relative water content, and photosynthetic efficiency. Under salt stress conditions, inoculation with Qhu-G9 resulted in notable increases in total biomass, root length, and plant height. Biochemical analyses further confirmed that Qhu-G9 alleviates the oxidative damage induced by salt stress by boosting antioxidant enzyme activities, reducing peroxide levels, and promoting the accumulation of osmotic regulators. These findings suggest that Qhu-G9 holds great promise as a PGPR that not only promotes plant growth, but also enhances plant tolerance to salt stress; thus, it has significant agricultural potential. Full article

Plant growth-promoting rhizobacteria (PGPR) are beneficial soil microorganisms that enhance plant growth and stress tolerance through various mechanisms, including phytohormone production, EPS production, phosphate solubilization, and extracellular enzyme production. These bacteria establish endosymbiotic relationships with plants, improving nutrient availability and overall crop productivity. Despite extensive research on PGPR isolation, their practical application in agricultural fields has faced challenges due to environmental stresses and limited survival during storage. To address these limitations, the present study aimed to isolate salt-tolerant bacterial strains and formulate them with organic carriers to enhance their stability and effectiveness under saline conditions. The isolated bacterial strains exhibited high salt tolerance, surviving NaCl concentrations of up to 850 millimolar. These strains demonstrated basic key plant growth-promoting traits, including phosphate solubilization, auxin production, and nitrogen fixation. The application of carrier-based formulations with both strains, Bacillus wiedmannii (RR2) and Bacillus paramobilis (RR3), improved physiological and biochemical parameters in wheat plants subjected to salinity stress. The treated plants, when subjected to salinity stress, showed notable increases in chlorophyll a (73.3% by Peat + RR3), chlorophyll b (41.1% by Compost + RR3), carotenoids (51.1% by Peat + RR3), relative water content (77.7% by Compost + RR2), proline (75.8% by compost + RR3), and total sugar content (12.4% by peat + RR2), as compared to the stressed control. Plant yield parameters such as stem length (35.1% by Peat + RR3), spike length (22.5% by Peat + RR2), number of spikes (67.6% by Peat + RR3), and grain weight (39.8% by Peat + RR3) were also enhanced and compared to the stressed control. These results demonstrate the potential of the selected salt-tolerant PGPR strains (ST-strains) to mitigate salinity stress and improve wheat yield under natural field conditions. The study highlights the significance of carrier-based PGPR applications as an effective and sustainable approach for enhancing crop productivity in saline-affected soils. Full article

Strain 53B2 was isolated from a commercial maize (Zea mays L.) field located in the Yaqui Valley, Mexico. Its draft genome comprises 5,844,085 bp, with a G + C content of 37.5%, an N50 of 602,122 bp, an L50 of 4, and a total of 129 contigs. Genome-based taxonomic affiliation showed this strain belonged to Priestia megaterium. Genome annotation revealed 6394 coding DNA sequences (CDSs), organized into 332 subsystems. Among these, several CDSs were associated with traits relevant to plant growth promotion, including categories such as iron acquisition and metabolism (40 CDSs) and secondary metabolism (6 CDSs), among others. In vitro metabolic assays supported genomic predictions, confirming the strain’s ability to produce IAA, solubilize phosphate, and tolerate abiotic stress. Additionally, greenhouse trials demonstrated that inoculation with Priestia megaterium 53B2 significantly enhanced plant growth parameters (p ≤ 0.05) versus uninoculated control: stem height increased by 22.8%, root length by 35.7%, stem and root fresh weights by 39.6% and 66.1%, and stem and root dry weights by 33.7% and 44.7%, respectively. This first report on the beneficial potential of Priestia megaterium 53B2 highlights its potential as a sustainable bioinoculant for maize cultivation. Full article

Globally, phosphogypsum (PG) is the primary by-product of the phosphorus industry. Aspergillus niger (A. niger), one of the most powerful types of phosphate-solubilizing fungi (PSF), can secrete organic acids to dissolve the phosphates in PG. This study investigated heavy metal (HM) remediation by PG and A. niger under the co-existence of Pb and Cd. It demonstrated that 1 mmol/L Pb²⁺ stimulated the bioactivity of A. niger during incubation, based on the CO₂ emission rate. PG successfully functioned as P source for the fungus, and promoted the growth of the fungal cells. Meanwhile, it also provided sulfates to immobilize Pb in the solution. The subsequently generated anglesite was confirmed using SEM imaging. The immobilization rate of Pb reached over 95%. Under co-existence, Pb²⁺ and 0.01 mmol/L Cd²⁺ maximized the stimulating effect of A. niger. However, the biotoxicity of Pb²⁺ and elevated Cd²⁺ (0.1 mmol/L) counterbalanced the stimulating effect. Finally, 1 mmol/L Cd²⁺ dramatically reduced the fungal activity. In addition, organic matters from the debris of A. niger could still bind Pb²⁺ and Cd²⁺ according to the significantly lowered water-soluble Pb and Cd concentrations. In all treatments with the addition of Cd²⁺, the relatively high biotoxicity of Cd²⁺ induced A. niger to absorb more Pb²⁺ to minimize the sorption of Cd²⁺ based on the XRD results. The functional group analysis of ATR-IR also confirmed the phenomenon. This pathway maintained the stability of Pb²⁺ immobilization using the fungus and PG. This study, hence, shed light on the application of A. niger and solid waste PG to remediate the pollution of Pb and Cd. Full article

Phosphate-solubilizing microbes (PSMs) in soil play a crucial role in converting insoluble phosphates into plant-available soluble phosphorus. This paper systematically presents a comprehensive array of qualitative and quantitative techniques to assess the phosphate-decomposing capabilities of microbes. Additionally, it introduces two optimized media, namely improved Monkina medium No. 1 and No. 2, which are particularly suitable for detecting the solubilization abilities of microbes toward insoluble organic phosphates. Talaromyces nanjingensis, a novel fungal species recently isolated from the rhizosphere soil of Pinus massoniana, demonstrates remarkable phosphate-solubilizing abilities. Across multiple temperature gradients (15 °C, 20 °C, 25 °C, 30 °C, and 37 °C), it effectively decomposes both insoluble inorganic and organic phosphates. This is achieved through the secretion of organic acids, including gluconic acid (6.10 g L⁻¹), oxalic acid (0.93 g L⁻¹), and malonic acid (0.17 g L⁻¹), as well as phosphate-solubilizing enzymes. Moreover, under low-, medium-, and high-temperature conditions, T. nanjingensis can decompose insoluble phosphates in three types of soil with varying pH levels, thereby enhancing the overall soil fertility. Genomic analysis of T. nanjingensis has identified approximately 308 genes associated with phosphate decomposition and environmental adaptability, validating its superior capabilities and multi-faceted strategies for phosphate mobilization. These findings underscore the wide applicability of T. nanjingensis in maintaining soil phosphorus homeostasis and optimizing the phosphorus use efficiency, highlighting its promising potential for agricultural and environmental applications. Full article

The major objective was to investigate the protective capabilities of endophytic bacterial strains isolated from a number of medicinal plant species towards Aspergillus spp. secured from the internal tissues of fungi-infected peanuts. Among 32 fungal isolates surveyed for mycotoxin production in various culture media (PDA, RBCA, YES, CA), 10 isolates qualitatively producing AFB₁, besides 10 OTA-producers, were assayed by HPLC for quantitative toxin production. Aspergillus spp. isolate Be 13 produced an extraordinary quantity of 1859.18 μg mL⁻¹ AFB₁, against the lowest toxin level of 280.40 μg mL⁻¹ produced by the fungus isolate IS 4. The estimated amounts of OTA were considerably lower and fell in the range 0.88–6.00 μg mL⁻¹; isolate Sa 1 was superior, while isolate Be 7 seemed inferior. Based on ITS gene sequencing, the highly toxigenic Aspergillus spp. isolates Be 13 and Sa 1 matched the description of A. novoparasiticus and A. ochraceus, respectively, ochraceus, respectively, which are present in GenBank with identity exceeding 99%. According to 16S rRNA gene sequencing, these antagonists labeled Ar6, Ma27 and So34 showed the typical characteristics of Pseudomonas aeruginosa, Bacillus subtilis and Bacillus velezensis, respectively, with similarity percentages of 99–100. The plant growth-promoting activity measurements of the identified endophytes indicated the production of 16.96–80.00 μg/100 mL culture medium of IAA. Phosphate-solubilizing capacity varied among endophytes from 2.50 to 21.38 μg/100 mL. The polysaccharide production pool of bacterial strains ranged between 2.74 and 6.57 mg mL⁻¹. P. aeruginosa Ar6 and B. velezensis successfully produced HCN, but B. subtilis failed. The in vitro mycotoxin biodegradation potential of tested bacterial endophytes indicated the superiority of B. velezensis in degrading both mycotoxins (AFB₁-OTA) with average percentage of 88.7; B. subtilis ranked thereafter (85.6%). The 30-day old peanut (cv. Giza 6) seedlings grown in gnotobiotic system severely injured due to infection with AFB₁/OTA-producing fungi, an effect expressed in significant reductions in shoot and root growth traits. Simultaneous treatment with the endophytic antagonists greatly diminished the harmful impact of the pathogens; B. velezensis was the pioneer, not P. aeruginosa Ar6. In conclusion, these findings proved that several endophytic bacterial species have the potential as alternative tools to chemical fungicides for protecting agricultural commodities against mycotoxin-producing fungi. Full article

The purpose of this study was to investigate the growth-promoting effects of four rhizobacterial isolates (RS60, RS65, RS46, and RP6) isolated from the tomato rhizosphere. These isolates were screened for key plant growth-promoting rhizobacteria (PGPR) mechanisms, including ammonia production, nitrogen fixation, phosphate solubilization, indole-3-acetic acid (IAA) production, and siderophore synthesis. Their potential to enhance seed germination and tomato plant growth was investigated in controlled and greenhouse conditions. Four isolates exhibited multiple PGPR attributes, notably IAA and ammonia production as well as phosphate solubilization. The results revealed that these strains significantly enhanced tomato seed germination and shoot growth in vitro, with RS65 showing the highest germination rate (70%). However, no significant differences in early seedling responses were observed under greenhouse conditions when compared to the control. Thirty days after inoculation, greenhouse results revealed that the four studied strains significantly increased growth metrics including shoot length, number of leaves, collar diameter, and dry weight. The isolate RP6 showed a significant effect on the growth of the plant, with an average shoot length of 34.40 cm and nine leaves per plant. In vitro antagonism assays demonstrated that isolates RS60, RS65, and RP6 effectively inhibited the growth of Botrytis cinerea, Alternaria alternata, and Oidium lycopersici, with inhibition rates exceeding 65%. These antagonistic activities were linked to the production of hydrolytic enzymes (chitinase, cellulase, pectinase, protease), siderophores, and hydrogen cyanide (HCN). Molecular identification through 16S rRNA gene sequencing confirmed the isolates as Bacillus cereus (RS60), Bacillus pumilus (RS46), Bacillus amyloliquefaciens (RP6), and Bacillus velezensis (RS65), each showing over 97% sequence similarity with reference strains. These findings underscore the potential of the selected Bacillus spp. as promising biofertilizers and biocontrol agents for sustainable tomato cultivation and support their inclusion in integrated disease and nutrient management strategies. Full article

The Hetao irrigation area is one of the largest irrigation areas in the Yellow River Basin and a typical salinized agricultural area. Crop type shifts in this area can alter soil phosphorus (P) morphology and microbial functional diversity, thereby influencing soil P losses. However, few studies have elucidated the underlying mechanisms. In this study, soil samples were collected from four different crop planting areas: sunflower field (SF), corn field (CF), wheat land (WL), and vegetable and fruit land (VFL). Subsequently, the physicochemical properties, P fractions, and phosphate-solubilizing microorganisms (PSMs) were analyzed. The results indicated that when other lands shifted to SF, the soil pH increased significantly. Simultaneously, SOM, TN, and TP decreased significantly during the crop type conversion. Analysis of P fraction revealed that moderately active P, including NaOH-P_i, NaOH-P_o, and HCl-P_i, were the dominant fractions in the tested soils. Among them, HCl-P_i was the major component of moderately active P. The soil P leaching change point in the tested are was 6.25 mg Olsen-P kg⁻¹. The probabilities of P leaching in WL, VFL, CF, and SF were 91.7%, 83.8%, 83.8%, and 66.7%, respectively. Additionally, the sum of the relative abundances of the three PSMs in SF, VFL, WL, and CF were 8.81%, 11.88%, 8.03%, and 10.29%, respectively. The shift in crop type to SF exacerbated the soil degradation process. Both TP and residual P in the soil decreased. However, the NaHCO₃ slightly increased, which may have been due to the increased abundance of Thiobacillus and Escherichia. Full article

Aims: Soil compaction is one of the main challenges in agriculture, negatively affecting cotton growth (Gossypium hirsutum L.), nutrition, and productivity. This study evaluated the efficacy of plant growth-promoting bacteria (PGPB), Exiguobacterium sibiricum, and Pantoea vagans in mitigating the effects of different soil compaction levels (65%, 75%, 85%, and 95%) on cotton performance. Methods: Parameters such as plant height, stem diameter, number of leaves, shoot dry matter (SDM), and nutrient content in leaves, stems, and roots were assessed. The methodology included variance analysis and mean clustering to identify significant differences among treatments using R software. Results: The results indicated that PGPB inoculation improved plant growth and nutrition even under high compaction levels. Cotton height increased by up to 45% in compacted soils (95%), while stem diameter and SDM also showed significant gains. Foliar nutrient levels of N (37.2 g kg⁻¹), Ca, and Mg remained within the adequate range for cotton cultivation, reflecting the efficiency of PGPB in enhancing nutrient absorption. Under severe compaction, Ca accumulation dropped to 18.2 g kg⁻¹, highlighting the physical constraints imposed on the roots; however, the bacterial action mitigated this impact. Additionally, bacterial strains increased the availability of N and P in the soil due to their ability to fix nitrogen, solubilize phosphates, and produce exopolysaccharides that improve soil structure. Conclusions: In conclusion, inoculation with Exiguobacterium sibiricum and Pantoea vagans is an effective strategy to mitigate the impacts of soil compaction on cotton. These bacteria promote plant growth and nutrition and enhance the soil’s physical and biological properties. Full article

Dinoflagellates significantly contribute to the carbon fixation and microbial loop in the ocean with high ecological diversity. While the microbial communities associated with the HABs of dinoflagellates have attracted intensive attention in recent years, little attention has been paid to the microbiomes associated with resting cysts, an important stage in the life cycle and bloom initiation dynamics of dinoflagellates. Using Scrippsiella acuminata as a representative of cyst producers and cyst-relevant research in dinoflagellates, we surveyed the bacteria and fungi microbiomes long associated with different life cycle stages of the dinoflagellate culture through 16S and ITS rRNA amplicon sequencing, and predicted their possible functions using the PICRUSt2 algorithm. The results found high species diversity of the associated bacteria–fungi microbiomes, and species featured with diverse and flexible metabolic capabilities that have stably co-occurred with the laboratory culture of S. acuminata. The host-attached and the free-living groups of bacteria–fungi microbiomes, as operationally defined in the context, showed significant differences in terms of their nutritional preferences. The bacteria–fungi species diversity and community structure associated with cysts are also distinguished significantly from that with vegetative cells, with the latter attracting more bacteria–fungi species specializing in phosphate solubilization. These results suggest that the relative species abundance and thus the community structure of the host-associated microbiome shift with the transition of life cycle stages and environmental conditions. Our findings show the association tightness between bacteria–fungi microbiomes and dinoflagellate hosts and the different life stages of hosts shaping the bacteria–fungi communities, which result in dynamic and specific interactions between bacteria–fungi microbiomes and their hosts. Full article

The low availability of phosphorus (P) in soil has become a critical factor limiting crop growth and agricultural productivity. This study aimed to isolate and evaluate a bacterial strain with high phosphate-solubilizing capacity to improve soil phosphorus utilization and promote crop growth. A phosphate-solubilizing bacterium, designated as YS-13, was isolated from farmland soil in Henan Province, China, and identified as Brevibacillus laterosporus based on morphological characteristics, physiological and biochemical traits, and 16S rDNA sequence analysis. Qualitative assessment using plate assays showed that strain YS-13 formed a prominent phosphate solubilization zone on organic and inorganic phosphorus media containing lecithin and calcium phosphate, with D/d ratios of 2.28 and 1.57, respectively. Quantitative evaluation using the molybdenum–antimony colorimetric method revealed soluble phosphorus concentrations of 21.24, 6.67, 11.73, and 17.05 mg·L⁻¹ when lecithin, ferric phosphate, calcium phosphate, and calcium phytate were used as phosphorus sources, respectively. The fermentation conditions for YS-13 were optimized through single-factor experiments combined with response surface methodology, using viable cell count as the response variable. The optimal conditions were determined as 34 °C, 8% inoculum volume, initial pH of 7.55, 48 h incubation, 5 g L⁻¹ NaCl, 8.96 g L⁻¹ glucose, and 8.86 g L⁻¹ peptone, under which the viable cell count reached 6.29 × 10⁸ CFU mL⁻¹, consistent with the predicted value (98.33%, p < 0.05). The plant growth-promoting effect of YS-13 was further validated through a pot experiment using Triticum aestivum cv. Jinchun 6. Growth parameters, including plant height, fresh biomass, root length, root surface area, root volume, and phosphorus content in roots and stems, were measured. The results demonstrated that YS-13 significantly enhanced wheat growth, with a positive correlation between bacterial concentration and growth indicators, although the growth-promoting effect plateaued at higher concentrations. This study successfully identified a high-efficiency phosphate-solubilizing strain, YS-13, and established optimal culture conditions and bioassay validation, laying a foundation for its potential application as a microbial inoculant and providing theoretical and technical support for reducing phosphorus fertilizer inputs and advancing sustainable agriculture. Full article