Eco-environmental responses of Eichhornia crassipes rhizobacteria community to co-stress of per(poly)fluoroalkyl substances and microplastics.

The stabilization of rhizobacteria communities plays a crucial role in sustaining healthy macrophyte growth. In light of increasing evidence of combined pollution from microplastics (MPs) and per- and polyfluoroalkyl substances (PFASs), Selecting typical floating macrophyte as a case, this study explored their impacts using hydroponic simulations and 16S rRNA high-throughput sequencing. A total of 31 phyla, 77 classes, 172 orders, 237 families, 332 genera, and 125 rhizobacteria species were identified. Proteobacteria (16.19% to 57.70%) was the dominant phylum, followed by Bacteroidota (12.34% to 44.48%) and Firmicutes (11.31% to 36.36%). In terms of α-diversity, polystyrene (PS) MPs and PFASs significantly impacted community abundance (ACE and PD-tree) rather than evenness (Shannon and Pielou) compared to the control. ßMNTD and ßNTI analyses revealed that PS MPs enhanced deterministic assembly processes driven by F-53B and GenX, while mitigating those induced by PFOA and PFOS. Contamination treatments narrowed the ecological niche breadths at both the phylum (5% (PS) to 49.91% (PS & PFOA)) and genus levels (8% (PS) to 63.96% (PS & PFOA)). Functionally, MPs and PFASs decreased the anaerobic capacity and ammonia nitrogen utilization of rhizosphere bacteria. This study enhances our understanding of the microecological responses of macrophyte-associated bacteria to combined MP and PFAS contamination and offers insights into ecological restoration strategies and mitigating associated environmental risks.

A "love match" score to compare root exudate attraction and feeding of the plant growth-promoting rhizobacteria Bacillus subtilis, Pseudomonas fluorescens, and Azospirillum brasilense.

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

Isolation, identification, and mechanism analysis of plant growth-promoting rhizobacteria in tobacco.

Plant growth, crop yield, and pest and disease control are enhanced by PGPR (Plant growth promoting rhizobacteria), which are beneficial microorganisms found in a close symbiosis with plant roots. Phytohormones are secreted, nutrient uptake is improved, and soil properties along with the microbiological environment are regulated by these microorganisms, making them a significant focus in agricultural research. In this study, the efficient PGPR strain T1 was isolated and screened from tobacco inter-root soil, and identified and confirmed by ITS sequencing technology. Tobacco growth indicators and soil property changes were observed and recorded through potting experiments. The activities of key enzymes (e.g., sucrase, catalase, urease) in soil were further determined. High-throughput sequencing technology was utilized to sequence the soil microbial community, and combined with macro-genomics analysis, the effects of T1 strain on soil microbial diversity and metabolic pathways were explored. Following the application of T1, significant improvements were observed in the height, leaf length, and width of tobacco plants. Furthermore, the physical and chemical properties of the soil were notably enhanced, including a 26.26% increase in phosphorus availability. Additionally, the activities of key soil enzymes such as sucrase, catalase, and urease were significantly increased, indicating improved soil health and fertility. Comprehensive joint microbiomics and macrogenomics analyses revealed a substantial rise in the populations of beneficial soil microorganisms and an enhancement in metabolic pathways, including amino acid metabolism, synthesis, and production of secondary metabolites. These increase in beneficial microorganisms and the enhancement of their metabolic functions are crucial for plant growth and soil fertility. This study provides valuable references for the development of innovative microbial fertilizers and offers programs for the sustainable development of modern agriculture.

Enhancing Maize Stress Tolerance and Productivity through Synergistic Application of Bacillus velezensis A6 and Lamiales Plant Extract, Biostimulants Suitable for Organic Farming.

Maize, a globally significant cereal, is increasingly cultivated under challenging environmental conditions, necessitating innovations in sustainable agriculture. This study evaluates the synergistic effects of a novel technique combining a Bacillus velezensis A6 strain with a plant extract from the Lamiales order on maize growth and stress resilience. Employing a pilot field trial, this study was conducted on the "La Añoreta" experimental farm of the ECONATUR group, where various biostimulant treatments, including bacterial and plant extract applications, were tested against a control group. The treatments were applied during key vegetative growth stages (V10-Tenth-Leaf, VT-Tassel, R1-Silking) and monitored for effects on plant height, biomass, and fumonisin content. The results suggest that the combined treatment of Bacillus velezensis A6 and the plant extract increases maize height (32.87%) and yield (62.93%) and also reduces fumonisin concentrations, improving its resistance to stress, compared to the control and other treatments. This study highlights the potential of microbial and botanical biostimulants and its novel combination for improving crop productivity and sustainability, suggesting that such synergistic combinations could play a crucial role in enhancing agricultural resilience to environmental stresses.

Plant growth-promoting rhizobacterial secondary metabolites in augmenting heavy metal(loid) phytoremediation: An integrated green in situ ecorestorative technology.

In recent times, increased geogenic and human-centric activities have caused significant heavy metal(loid) (HM) contamination of soil, adversely impacting environmental, plant, and human health. Phytoremediation is an evolving, cost-effective, environment-friendly, in situ technology that employs indigenous/exotic plant species as natural purifiers to remove toxic HM(s) from deteriorated ambient soil. Interestingly, the plant's rhizomicrobiome is pivotal in promoting overall plant nutrition, health, and phytoremediation. Certain secondary metabolites produced by plant growth-promoting rhizobacteria (PGPR) directly participate in HM bioremediation through chelation/mobilization/sequestration/bioadsorption/bioaccumulation, thus altering metal(loid) bioavailability for their uptake, accumulation, and translocation by plants. Moreover, the metallotolerance of the PGPR and the host plant is another critical factor for the successful phytoremediation of metal(loid)-polluted soil. Among the phytotechniques available for HM remediation, phytoextraction/phytoaccumulation (HM mobilization, uptake, and accumulation within the different plant tissues) and phytosequestration/phytostabilization (HM immobilization within the soil) have gained momentum in recent years. Natural metal(loid)-hyperaccumulating plants have the potential to assimilate increased levels of metal(loid)s, and several such species have already been identified as potential candidates for HM phytoremediation. Furthermore, the development of transgenic rhizobacterial and/or plant strains with enhanced environmental adaptability and metal(loid) uptake ability using genetic engineering might open new avenues in PGPR-assisted phytoremediation technologies. With the use of the Geographic Information System (GIS) for identifying metal(loid)-impacted lands and an appropriate combination of normal/transgenic (hyper)accumulator plant(s) and rhizobacterial inoculant(s), it is possible to develop efficient integrated phytobial remediation strategies in boosting the clean-up process over vast regions of HM-contaminated sites and eventually restore ecosystem health.

Predatory protists impact plant performance by promoting plant growth-promoting rhizobacterial consortia.

Plant performance is impacted by rhizosphere bacteria. These bacteria are subjected to both bottom-up control by root exudates as well as top-down control by predators, particularly protists. Protists stimulate plant growth-promoting microbes resulting in improved plant performance. However, knowledge of the mechanisms that determine the interconnections within such tripartite protist-bacteria-plant interactions remains limited. We conducted experiments examining the effects of different densities of the predatory protist Cercomonas lenta on rhizosphere bacterial communities, specifically zooming on interactions between Cercomonas lenta and key bacterial taxa, as well as interactions among key bacterial taxa. We tracked rhizosphere bacterial community composition, potential microbial interactions, and plant performance. We found that Cercomonas lenta inoculation led to an average increase in plant biomass of 92.0%. This effect was linked to an increase in plant growth-promoting rhizobacteria (Pseudomonas and Sphingomonas) and a decrease in bacteria (Chitinophaga) that negatively impact on plant growth-promoting rhizobacteria. We also found evidence for cooperative enhancements in biofilm formation within the plant growth-promoting rhizobacterial consortium. Cercomonas lenta enhanced a plant growth-promoting rhizobacterial consortium colonization by promoting its cooperative biofilm formation in the rhizosphere, leading to a 14.5% increase in phosphate solubilization that benefits plant growth. Taken together, we provide mechanistic insights into how the predatory protist Cercomonas lenta impacts plant growth, namely by stimulating plant beneficial microbes and enhancing their interactive activities such as biofilm formation. Predatory protists may therefore represent promising biological agents that can contribute to sustainable agricultural practices by promoting interactions between the plant and its microbiome.

Identification of Stutzerimonas stutzeri volatile organic compounds that enhance the colonization and promote tomato seedling growth.

AIMS: Volatile organic compounds (VOCs) have an important function in plant growth-promoting rhizobacteria (PGPR) development and plant growth. This study aimed to identify VOCs of the PGPR strain, Stutzerimonas stutzeri NRCB010, and investigate their effects on NRCB010 biofilm formation, swarming motility, colonization, and tomato seedling growth. METHODS AND RESULTS: Solid-phase microextraction and gas chromatography-mass spectrometry were performed to identify the VOCs produced during NRCB010 fermentation. A total of 28 VOCs were identified. Among them, seven (e.g. γ-valerolactone, 3-octanone, mandelic acid, 2-heptanone, methyl palmitate, S-methyl thioacetate, and 2,3-heptanedione), which smell well, are beneficial for plant, or as food additives, and without serious toxicities were selected to evaluate their effects on NRCB010 and tomato seedling growth. It was found that most of these VOCs positively influenced NRCB010 swarming motility, biofilm formation, and colonization, and the tomato seedling growth. Notably, γ-valerolactone and S-methyl thioacetate exhibited the most positive performances. CONCLUSION: The seven NRCB010 VOCs, essential for PGPR and crop growth, are potential bioactive ingredients within microbial fertilizer formulations. Nevertheless, the long-term sustainability and replicability of the positive effects of these compounds across different soil and crop types, particularly under field conditions, require further investigation.

Genetic diversity, stress tolerance and phytobeneficial potential in rhizobacteria of Vachellia tortilis subsp. raddiana.

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

Bacillus licheniformisYB06: A Rhizosphere-Genome-Wide Analysis and Plant Growth-Promoting Analysis of a Plant Growth-Promoting Rhizobacterium Isolated from Codonopsis pilosula.

Codonopsis pilosula, commonly known as Dangshen, is a valuable medicinal plant, but its slow growth and susceptibility to environmental stress pose challenges for its cultivation. In pursuit of sustainable agricultural practices to enhance the yield and quality of Dangshen, the present study isolated a bacterial strain exhibiting plant growth-promoting potential from the rhizosphere of C. pilosula. This strain was subsequently identified as Bacillus licheniformisYB06. Assessment of its plant growth-promoting attributes revealed the potential of B. licheniformis YB06 as a biofertilizer. Whole-genome sequencing of B. licheniformis YB06 revealed a genome size of 4,226,888 bp with a GC content of 46.22%, harboring 4325 predicted protein-coding sequences. Genomic analysis of B. licheniformis YB06 revealed a diverse array of genes linked to induced systemic resistance (ISR) and plant growth-promoting (PGP) traits, encompassing phytohormone production, nitrogen assimilation and reduction, siderophore biosynthesis, phosphate solubilization, biofilm formation, synthesis of PGP-related amino acids, and flagellar motility. Seed germination assays demonstrated the positive effects of B. licheniformis YB06 on the germination and growth of C. pilosula seedlings. Furthermore, we explored various fertilization regimes, particularly the B. licheniformis YB06-based biofertilizer, were investigated for their impact on the structure and diversity of the C. pilosula rhizosphere soil bacterial community. Our findings revealed that fertilization significantly impacted soil bacterial composition and diversity, with the combined application of B. licheniformis YB06-based biofertilizer and organic fertilizer exhibiting a particularly pronounced enhancement of rhizosphere bacterial community structure and diversity. This study represents the first report on the beneficial effects of B. licheniformis YB06 on both the growth of C. pilosula and the composition of its rhizosphere soil microbial community. These findings provide a theoretical foundation and practical guidance for the development of novel bio-organic compound fertilizers, thereby contributing to the sustainable cultivation of C. pilosula.

Optimizing crop quality and yield: Assessing the impact of integrated potassium management on Chinese cabbage (Brassica rapa L. subsp. chinensis).

Potassium, a pivotal macronutrient essential for growth, development, and crop yield, serves as a critical determinant of soil productivity. Its depletion disrupts the equilibrium of soil nutrients, prompting an investigation into integrated potassium management strategies to address this challenge. A field experiment was conducted during the winter season of 2020 using a randomized complete block design, with eight treatments, each replicated three times in Chinese cabbage (Brassica rapa L. subsp. chinensis). These treatments comprised standard (100 %) and reduced (75 % and 50 %) rates of the recommended dose of potassium (RDK) via muriate of potash (MOP). Variations in the inclusion and exclusion of plant growth-promoting rhizobacteria (PGPR), farmyard manure (FYM) as 25 % of the potassium recommendation, and foliar spray of nano potash were systematically implemented. Findings unequivocally demonstrated that the treatmentT8, involving 100 % RDK +25 % K through FYM + PGPR + nano K fertilizer spray at 25 and 40 DAS, yielded significant improvements in both green fodder (64.0 t ha-1) and dry fodder (7.87 t ha-1).Moreover, T8 exhibited the highest values for total ash (8.75 %), total ash yield (68.9 ± 2.88 kg ha-1), ether extract (2.85 %), ether extract yield (22.4 ± 0.88 kg ha-1), crude protein (9.71 %), and total crude protein yield (76.4 ± 3.21 kg ha-1). Conversely, a marked reduction was observed in various fiber components and carbohydrate fractions upon application of the T8 treatment. The lowest values of yield, crude protein content, total ash ether extract were recorded in treatment T1 (control) applied with no potassium. This investigation underscores the inadequacy of the recommended potassium dose in achieving optimal productivity, necessitating a re-evaluation of potassium fertilization levels. The integrated approach involving FYM, PGPR, and nano potash, coupled with the recommended potassium dose through MOP, emerges as a promising avenue for augmenting both yield and quality parameters in Chinese cabbage.

Synergistic effect of Pseudomonas putida and endomycorrhizal inoculation on the physiological response of onion (Allium cepa L.) to saline conditions.

Salinity stress negatively affects the growth and yield of crops worldwide. Onion (Allium cepa L.) is moderately sensitive to salinity. Beneficial microorganisms can potentially confer salinity tolerance. This study investigated the effects of endomycorrhizal fungi (M), Pseudomonas putida (Ps) and their combination (MPs) on onion growth under control (0 ppm), moderate (2000 ppm) and high (4000 ppm) NaCl salinity levels. A pot experiment was conducted with sandy loam soil and onion cultivar Giza 20. Results showed that salinity reduced growth attributes, leaf pigments, biomass and bulb yield while increasing oxidative stress markers. However, individual or combined inoculations significantly increased plant height, bulb diameter and biomass production compared to uninoculated plants under saline conditions. MPs treatment provided the highest stimulation, followed by Pseudomonas and mycorrhizae alone. Overall, dual microbial inoculation showed synergistic interaction, conferring maximum benefits for onion growth, bulbing through integrated physiological and biochemical processes under salinity. Bulb yield showed 3.5, 36 and 83% increase over control at 0, 2000 and 4000 ppm salinity, respectively. In conclusion, combined application of mycorrhizal-Pseudomonas inoculations (MPs) effectively mitigate salinity stress. This approach serves as a promising biotechnology for ensuring sustainable onion productivity under saline conditions.

Effect of a Bacillus velezensis and Lysinibacillus fusiformis-based biofertilizer on phosphorus acquisition and grain yield of soybean.

Introduction: Phosphate-solubilizing bacteria that function through acidification (organic acid synthesis) or mineralization (production of enzymes such as phytase and phosphatases) have been explored as a biotechnological alternative to enhance plant access to phosphorus (P) retained in organic and inorganic forms in agricultural soils. This study tested the hypothesis that applying a biofertilizer composed of a recognized phosphate-solubilizing bacterium (Bacillus velezensis - endophytic strain BVPS01) and an underexplored plant growth-promoting bacterium (Lysinibacillus fusiformis - endophytic strain BVPS02) would improve the growth and grain yield of Glycine max L. plants. Methods: Initial in vitro tests assessed the functional traits of these bacteria, and a mix of strains BVPS01 and BVPS02 was produced and tested under field conditions to evaluate its agronomic efficiency. Results: The results confirmed the hypothesis that the tested biofertilizer enhances the agronomic performance of G. max plants in the field. The B. velezensis strain (BVPS01) was found to be more effective than the L. fusiformis strain (BVPS02) in solubilizing phosphates via the phosphatase enzyme production pathway, indicated by the expression of the phoC and phoD genes. In contrast, L. fusiformis was more effective in solubilizing phosphates through organic acid and phytase-related pathways, in addition to synthesizing indole-3-acetic acid and increasing the mitotic index in the root meristem of G. max plants. These strains exhibited biological compatibility, and the formulated product based on these rhizobacteria enhanced root development and increased the number of nodules and flowers, positively affecting 1000-grain weight, grain yield, and grain P content. Discussion: Thus, the tested biofertilizer demonstrated potential to improve root growth and increase both the yield and quality of soybean crops, making it a sustainable and low-cost strategy.

Reduced fertilization supplemented with Bacillus safensis RGM 2450 and Bacillus siamensis RGM 2529 promotes tomato production in a sustainable way.

The rising demand for vegetables has driven the adoption of greenhouse cultivation to guarantee high yields and quality of fresh produce year-round. Consequently, this elevates the demand for fertilizers, whose costs are progressively escalating. Bacillus safensis RGM 2450 and Bacillus siamensis RGM 2529 are plant growth-promoting rhizobacteria (PGPR). The combination of these strains exhibited synergistic activity in stimulating the growth and seedling hydration of tomatoes. In this study, the effects of inoculation with a RGM 2450 plus RGM 2529 formulation were evaluated under 66% and 100% fertilization programs in tomato crops under greenhouse conditions. Fertilization programs (66% and 100%) with or without commercial biostimulants were used as control treatments. In this assay, the NPK percentage in the plant tissue, tomato average weight, tomato average weight per harvest, tomato diameter, and changes in the colonization, structure, and diversity of the bacterial rhizosphere were measured. The 100% and 66% fertilization programs supplemented with the RGM 2529 plus RGM 2450 formulation increased the average weight of tomatoes per harvest without statistical difference between them, but with the other treatments. The 66% fertilization with RGM 2450 plus RGM 2529 increased between 1.5 and 2.0 times the average weight of tomatoes per harvest compared to the 66% and 100% fertilizations with and without commercial biostimulant treatments, respectively. This study represents the first report demonstrating that the application of a formulation based on a mixture of B. siamensis and B. safensis in a fertilization program reduced by 33% is equivalent in productivity to a conventional fertilization program for tomato cultivation, achieving an increase in potential plant growth-promoting rizobacteria of the genus Flavobacterium. Therefore, the adoption of a combination of these bacterial strains within the framework of a 66% inorganic fertilization program is a sustainable approach to achieving greater tomato production and reducing the environmental risks associated with the use of inorganic fertilization.

Pseudochrobactrum asaccharolyticum mitigates arsenic induced oxidative stress of maize plant by enhancing water status and antioxidant defense system.

BACKGROUND: Oxidative stress mediated by reactive oxygen species (ROS) is a common denominator in arsenic toxicity. Arsenic stress in soil affects the water absorption, decrease stomatal conductance, reduction in osmotic, and leaf water potential, which restrict water uptake and osmotic stress in plants. Arsenic-induced osmotic stress triggers the overproduction of ROS, which causes a number of germination, physiological, biochemical, and antioxidant alterations. Antioxidants with potential to reduce ROS levels ameliorate the arsenic-induced lesions. Plant growth promoting rhizobacteria (PGPR) increase the total soluble sugars and proline, which scavenging OH radicals thereby prevent the oxidative damages cause by ROS. The main objective of this study was to evaluate the potential role of Arsenic resistant PGPR in growth of maize by mitigating arsenic stress. METHODOLOGY: Arsenic tolerant PGPR strain MD3 (Pseudochrobactrum asaccharolyticum) was used to dismiss the 'As' induced oxidative stress in maize grown at concentrations of 50 and 100 mg/kg. Previously isolated arsenic tolerant bacterial strain MD3 "Pseudochrobactrum asaccharolyticum was used for this experiment. Further, growth promoting potential of MD3 was done by germination and physio-biochemical analysis of maize seeds. Experimental units were arranged in Completely Randomized Design (CRD). A total of 6 sets of treatments viz., control, arsenic treated (50 & 100 mg/kg), bacterial inoculated (MD3), and arsenic stress plus bacterial inoculated with three replicates were used for Petri plates and pot experiments. After treating with this MD3 strain, seeds of corn were grown in pots filled with or without 50 mg/kg and 100 mg/kg sodium arsenate. RESULTS: The plants under arsenic stress (100 mg/kg) decreased the osmotic potential (0.8 MPa) as compared to control indicated the osmotic stress, which caused the reduction in growth, physiological parameters, proline accumulation, alteration in antioxidant enzymes (Superoxide dismutase-SOD, catalase-CAT, peroxidase-POD), increased MDA content, and H2O2 in maize plants. As-tolerant Pseudochrobactrum asaccharolyticum improved the plant growth by reducing the oxidation stress and antioxidant enzymes by proline accumulation. PCA analysis revealed that all six treatments scattered differently across the PC1 and PC2, having 85.51% and 9.72% data variance, respectively. This indicating the efficiency of As-tolerant strains. The heatmap supported the As-tolerant strains were positively correlated with growth parameters and physiological activities of the maize plants. CONCLUSION: This study concluded that Pseudochrobactrum asaccharolyticum reduced the 'As' toxicity in maize plant through the augmentation of the antioxidant defense system. Thus, MD3 (Pseudochrobactrum asaccharolyticum) strain can be considered as bio-fertilizer.

Plant growth-promoting rhizobacterium Bacillus megaterium modulates the expression of antioxidant-related and drought-responsive genes to protect rice (Oryza sativa L.) from drought.

Global climate change poses a significant threat to plant growth and crop yield and is exacerbated by environmental factors, such as drought, salinity, greenhouse gasses, and extreme temperatures. Plant growth-promoting rhizobacteria (PGPR) help plants withstand drought. However, the mechanisms underlying PGPR-plant interactions remain unclear. Thus, this study aimed to isolate PGPR, Bacillus megaterium strains CACC109 and CACC119, from a ginseng field and investigate the mechanisms underlying PGPR-stimulated tolerance to drought stress by evaluating their plant growth-promoting activities and effects on rice growth and stress tolerance through in vitro assays, pot experiments, and physiological and molecular analyses. Compared with B. megaterium type strain ATCC14581, CACC109 and CACC119 exhibited higher survival rates under osmotic stress, indicating their potential to enhance drought tolerance. Additionally, CACC109 and CACC119 strains exhibited various plant growth-promoting activities, including phosphate solubilization, nitrogen fixation, indole-3-acetic acid production, siderophore secretion, 1-aminocyclopropane-1-carboxylate deaminase activity, and exopolysaccharide production. After inoculation, CACC109 and CACC119 significantly improved the seed germination of rice (Oryza sativa L.) under osmotic stress and promoted root growth under stressed and non-stressed conditions. They also facilitated plant growth in pot experiments, as evidenced by increased shoot and root lengths, weights, and leaf widths. Furthermore, CACC109 and CACC119 improved plant physiological characteristics, such as chlorophyll levels, and production of osmolytes, such as proline. In particular, CACC109- and CACC119-treated rice plants showed better drought tolerance, as evidenced by their higher survival rates, greater chlorophyll contents, and lower water loss rates, compared with mock-treated rice plants. Application of CACC109 and CACC119 upregulated the expression of antioxidant-related genes (e.g., OsCAT, OsPOD, OsAPX, and OsSOD) and drought-responsive genes (e.g., OsWRKY47, OsZIP23, OsDREB2, OsNAC066, OsAREB1, and OsAREB2). In conclusion, CACC109 and CACC119 are promising biostimulants for enhancing plant growth and conferring resistance to abiotic stresses in crop production. Future studies should conduct field trials to validate these findings under real agricultural conditions, optimize inoculation methods for practical use, and further investigate the biochemical and physiological responses underlying the observed benefits.

Tracking maize colonization and growth promotion by Azospirillum reveals strain-specific behavior and the influence of inoculation method.

Inoculation of Azospirillum in maize has become a standard practice in Latin America. However, information on the behavior and population survival of the Azospirillum post-inoculation is scarce, making standardization difficult and generating variations in inoculation efficiency across assays. In this study, we tracked the colonization of three agriculturally relevant Azospirillum strains (Ab-V5, Az39, and the ammonium excreting HM053) after different inoculation methods in maize crops by qPCR. Besides, we assessed their ability to promote maize growth by measuring biometric parameters after conducting a greenhouse essay over 42 days. Inoculated plants exhibited Azospirillum population ranging from 103 to 107 cells plant-1 throughout the experiment. While all strains efficiently colonized roots, only A. argentinense Az39 demonstrated bidirectional translocation between roots and shoots, which characterizes a systemic behavior. Optimal inoculation methods for plant growth promotion varied among strains: soil inoculation promoted the best maize growth for the Ab-V5 and Az39 strains, while seed inoculation proved most effective for HM053. The findings of this study demonstrate that the inoculation method affects the behavior of Azospirillum strains and their effectiveness in promoting maize growth, thereby guiding practices to enhance crop yield.

Rhizoengineering with biofilm producing rhizobacteria ameliorates oxidative stress and enhances bioactive compounds in tomato under nitrogen-deficient field conditions.

Nitrogen (N) deficiency limits crop productivity. In this study, rhizoengineering with biofilm producing rhizobacteria (BPR) contributing to productivity, physiology, and bioactive contents in tomato was examined under N-deficient field conditions. Here, different BPR including Leclercia adecarboxylata ESK12, Enterobacter ludwigii ESK17, Glutamicibacter arilaitensis ESM4, E. cloacae ESM12, Bacillus subtilis ESM14, Pseudomonas putida ESM17 and Exiguobacterium acetylicum ESM24 were used for the rhizoengineering of tomato plants. Rhizoengineered plants showed significant increase in growth attributes (15.73%-150.13 %) compared to the control plants. However, production of hydrogen peroxide (21.49-59.38 %), electrolyte leakage (19.5-38.07 %) and malondialdehyde accumulation (36.27-46.31 %) were increased remarkably more in the control plants than the rhizoengineered plants, thus N deficiency induced the oxidative stress. Compared to the control, photosynthetic rate, leaf temperature, stomatal conductance, intrinsic and instantaneous water use efficiency, relative water content, proline and catalase activity were incredibly enhanced in the rhizoengineered plants, suggesting both non-enzymatic and enzymatic antioxidant systems might protect tomato plants from oxidative stress under N-deficient field conditions. Yield (10.24-66.21 %), lycopene (4.8-7.94 times), flavonoids (52.32-110.46 %), phenolics (9.79-23.5 %), antioxidant activity (34.09-86.36 %) and certain minerals were significantly increased in the tomatoes from rhizoengineered plants. The principal component analysis (PCA) revealed that tomato plants treated with BPR induced distinct profiles compared to the control. Among all the applied BPR strains, ESM4 and ESM14 performed better in terms of biomass production, while ESK12 and ESK17 showed better results for reducing oxidative stress and increasing bioactive compounds in tomato, respectively. Thus, rhizoengineering with BPR can be utilized to mitigate the oxidative damage and increase the productivity and bioactive compounds in tomato under N-deficient field conditions.

Isolation and Characterization of Plant Growth-Promoting Bacteria from the Rhizosphere of Medicinal and Aromatic Plant Minthostachys verticillata.

This study aimed to isolate and characterize Pseudomonas native strains from the rhizospheric soil of Minthostachys verticillata plants to evaluate their potential as plant growth-promoting rhizobacteria (PGPR). A total of 22 bacterial isolates were obtained and subjected to various biochemical tests, as well as assessments of plant growth-promoting traits such as phosphate solubilization, hydrogen cyanide production, biocontrol properties through antibiosis, and indole acetic production. Genotypic analysis via 16S rRNA gene sequencing and phylogenetic tree construction identified the strains, with one particular strain named SM 33 showing significant growth-promoting effects on M. verticillata seedlings. This strain, SM 33, showed high similarity to Stutzerimonas stutzeri based on 16S rRNA gene sequencing and notably increased both shoot fresh weight and root dry weight of the plants. These findings underscore the potential application of native Pseudomonas strains in enhancing plant growth and health, offering promising avenues for sustainable agricultural practices.

The Biotechnological Potential of Plant Growth-Promoting Rhizobacteria Isolated from Maize (Zea mays L.) Cultivations in the San Martin Region, Peru.

Maize (Zea mays L.) is an essential commodity for global food security and the agricultural economy, particularly in regions such as San Martin, Peru. This study investigated the plant growth-promoting characteristics of native rhizobacteria isolated from maize crops in the San Martin region of Peru with the aim of identifying microorganisms with biotechnological potential. Soil and root samples were collected from maize plants in four productive zones in the region: Lamas, El Dorado, Picota, and Bellavista. The potential of twelve bacterial isolates was evaluated through traits, such as biological nitrogen fixation, indole acetic acid (IAA) production, phosphate solubilization, and siderophore production, and a completely randomized design was used for these assays. A completely randomized block design was employed to assess the effects of bacterial strains and nitrogen doses on maize seedlings. The B3, B5, and NSM3 strains, as well as maize seeds of the yellow hard 'Advanta 9139' variety, were used in this experiment. Two of these isolates, B5 and NSM3, exhibited outstanding characteristics as plant growth promoters; these strains were capable of nitrogen fixation, IAA production (35.65 and 26.94 µg mL-1, respectively), phosphate solubilization (233.91 and 193.31 µg mL-1, respectively), and siderophore production (34.05 and 89.19%, respectively). Furthermore, molecular sequencing identified the NSM3 isolate as belonging to Sporosarcina sp. NSM3 OP861656, while the B5 isolate was identified as Peribacillus sp. B5 OP861655. These strains show promising potential for future use as biofertilizers, which could promote more sustainable agricultural practices in the region.

Harnessing rhizobacteria: Isolation, identification, and antifungal potential against soil pathogens.

Rhizobacteria play a crucial role in plant health by providing natural antagonism against soil-borne fungi. The use of rhizobacteria has been viewed as an alternative to the use of chemicals that could be useful for the integrated management of plant diseases and also increase yield in an environmentally friendly manner. However, there is limited understanding of the specific mechanisms by which rhizobacteria inhibit these pathogens and the diversity of rhizobacterial species involved. This study aims to isolate, identify, and characterize rhizobacteria with antagonistic activities against soil-borne fungi. Laboratory tests were carried out on isolated rhizobacteria to evaluate their inhibitory activity against Rhizoctonia solani, Pythium aphanidermatum and Macrophomina phaseolina. The selected bacteria were identified using the Vitek 2 compact system and 16S rRNA genes. Experiments were carried out to evaluate the plant growth promotion and biocontrol ability of these selected isolates. Out of 324 rhizobacteria isolates obtained from various plant species, twelve were chosen due to their strong (>50 %) wide-ranging antifungal activity against three significant phytopathogenic fungi species. According to the identification results, they belong to the following species: Aeribacillus pallidus ECC4, Alloiococcus otitis BRE6, Aneurinibacillus thermoaerophilus ECL1, A. thermoaerophilus SDV1, Bacillus halotolerans DMC8, B. megaterium SKE2, B. megaterium TNK1, B. subtilis NAS1, Enterobacter cloacae complex BZD3, Leclercia adecarboxylata DKS3, Paenibacillus polymyxa TRS4, and Staphylococcus lentus BZD2. Eleven isolates produced protease, six isolates produced chitinase, and seven isolates were highly effective in producing hydrogen cyanide. Ten isolates could fix nitrogen, while all isolates could produce potassium, indole-3-acetic acid, siderophore, and ammonia. These findings enhance our understanding of rhizobacterial biodiversity and their potential as biocontrol agents in sustainable agriculture.