Synergistic effects of biofilm-producing PGPR strains on wheat plant colonization, growth and soil resilience under drought stress

Synergistic effect of grassland plants and beneficial rhizosphere bacteria helps plants cope with overgrazing stress

BACKGROUND

Overgrazing (OG) is an important driver of grassland degradation and productivity decline. Highly effective synergy between plants and rhizosphere growth-promoting rhizobacteria (PGPR) may be a major way for grassland plants to effectively cope with OG stress. There have been few reports providing solid evidence on how this synergy occurs.

RESULT

This study combined with multi-omics analysis and the interaction effect of specific root exudate with PGPR B68, aiming to reveal the synergistic effect and regulatory mechanism of L. chinensis and PGPR under overgrazing stress. The results showed that Leymus chinensis plants with OG history can recruit the beneficial Phyllobacterium sp. B68 by regulating specific root exudate compounds(such as amino acid L-leucyl-L-alanine and alkaloid cordycepin). These compounds enhanced B68 rhizosphere colonization by promoting B68 chemotaxis and biofilm formation. The pot study experiments indicated that the bacterial isolates used as bio inoculants increased L. chinensis growth (mainly including plant height and biomass) by significantly increasing the chlorophyll content, RuBisCO activity, soluble sugar, plant hormones and nutrient content. Metagenomics results show that B68 inoculation significantly altered rhizosphere soil bacterial community composition and function. Additionally, B68 systemically upregulated the expression level of genes involved in plant hormone signaling, nutrient and sugar transporters, nitrogen metabolism, cell division, cell wall modification and photosynthesis to promote plant growth. The above results indicate that the PGPR B68 recruited by the root exudates of L. chinensis under OG helps the plant adapt to stress by promoting nutrient uptake and transport, maintaining hormone homeostasis, and enhancing the expression of genes related to plant growth and nutrient metabolism.

CONCLUSION

This study provides new insights into the positive interactions between grassland plants and rhizosphere bacteria under OG stress, offering valuable knowledge for developing new fertilizers and better management practices for degraded rangeland restoration and sustainable agriculture development.

CLINICAL TRIAL NUMBER

Not applicable.

Combined Transcriptomics and Metabolomics Uncover the Potential Mechanism of Plant Growth-Promoting Rhizobacteria on the Regrowth of Leymus chinensis After Mowing

Mowing significantly influences nutrient cycling and stimulates metabolic adjustments in plants to promote regrowth. Plant growth-promoting rhizobacteria (PGPR) are crucial for enhancing plant growth, nutrient absorption, and stress resilience; however, whether inoculation with PGPR after mowing can enhance plant regrowth capacity further, as well as its specific regulatory mechanisms, remains unexplored. In this study, PGPR Pantoea eucalyptus (B13) was inoculated into mowed Leymus chinensis to evaluate its effects on phenotypic traits, root nutrient contents, and hormone levels during the regrowth process and to further explore its role in the regrowth of L. chinensis after mowing. The results showed that after mowing, root nutrient and sugar contents decreased significantly, while the signal pathways related to stress hormones were activated. This indicates that after mowing, root resources tend to sacrifice a part of growth and prioritize defense. After mowing, B13 inoculation regulated the plant's internal hormone balance by reducing the levels and signal of JA, SA, and ABA and upregulated the signal transduction of growth hormones in the root, thus optimizing growth and defense in a mowing environment. Transcriptomic and metabolomic analyses indicated that B13 promoted nutrient uptake and transport in L. chinensis root, maintained hormone homeostasis, enhanced metabolic pathways related to carbohydrates, energy, and amino acid metabolism to cope with mowing stress, and promoted root growth and regeneration of shoot. This study reveals the regenerative strategy regulated by B13 in perennial forage grasses, helping optimize resource utilization, increase yield, and enhance grassland stability and resilience.

Significance of zinc-solubilizing plant growth-promoting rhizobacterial strains in nutrient acquisition, enhancement of growth, yield, and oil content of canola (Brassica napus L.)

The present study was conducted with the aim to isolate, characterize, and identify the promising zinc-solubilizing rhizobacteria found naturally in the rhizosphere of canola (Brassica napus L.) plants. The study investigated the roles of these strains in nutrient acquisition and assimilation of extracellular molecules such as hormones and secondary metabolites. Ten isolated promising zinc-solubilizing strains (CLS1, CLS2, CLS3, CLS6, CLS8, CLS9, CLS11, CLS12, CLS13, and CLS15) were selected and characterized biochemically. Almost all the tested strains were Gram-positive, could fix nitrogen, and were positive for indole acetic acid, HCN, exopolysaccharides, and siderophore production. These effective zinc-solubilizing strains were identified through 16S rRNA gene sequencing. Based on the amount of solubilized zinc and halo zone diameter, four potent strains (CLS1, CLS2, CLS3, and CLS9) were selected for pot and field evaluation. Among all the identified bacterial genera isolated from the rhizosphere of the same host plant at different sampling sites, Priestia aryabhattai was found most abundant and found at all three sampling sites. The strains Priestia megaterium, Staphylococcus succinus, and Bacillus cereus were found at two different sites. Bacillus subtilis was found at only one site. These strains have a number of plant growth-stimulating characteristics as well as the ability to colonize plant roots successfully. The results indicated that inoculation of all these four zinc-solubilizing tested strains enhanced the plant growth, oil contents, and yield attributes of canola as compared to non-inoculated control with fertilizer levels. Staphylococcus succinus (CLS1) was first reported as a zinc solubilizer and associated with canola. Priestia aryabhattai (CLS2) and Priestia megaterium (CLS9) were found to be the best strains, with the most pronounced beneficial effect on canola growth and yield traits in both pot and field conditions. The site-specific dominance of these strains observed in this study may contribute toward decision-making for the development of specific inocula for canola. Therefore, identification of these strains could help in providing adequate amount of soluble zinc along with enhanced plant growth, yield, and oil content of canola.

PGPR: Key to Enhancing Crop Productivity and Achieving Sustainable Agriculture

Due to the burgeoning global population and the advancement of economies, coupled with human activities leading to the degradation of soil ecosystems and the depletion of non-renewable resources, concerns have arisen regarding food security and human survival. In order to address these adverse impacts, the spotlight has been cast upon plant growth-promoting rhizobacteria (PGPR), driven by a strong environmental consciousness. PGPR possesses the capability to foster plant growth and amplify crop yield through both direct and indirect mechanisms. By expediting plant growth, augmenting nutrient assimilation, heightening crop yield and caliber, and fortifying stress resilience, the application of PGPR can mitigate reliance on chemical fertilizers and pesticides while diminishing ecological perils. This exposition delves into the function of PGPR in modulating plant hormones, fostering nutrient solubilization, and fortifying plant resistance against biotic and abiotic stressors. This review offers valuable insights into the intricate interplay between PGPR and plants, elucidating uncertainties ripe for further investigation. Profound comprehension and judicious utilization of PGPR are indispensable for attaining sustainable agricultural progression, making substantial contributions to resolving the conundrums of global food security and environmental conservation.

Role of Bacillus subtilis exopolymeric genes in modulating rhizosphere microbiome assembly

BACKGROUND

Bacillus subtilis is well known for promoting plant growth and reducing abiotic and biotic stresses. Mutant gene-defective models can be created to understand important traits associated with rhizosphere fitness. This study aimed to analyze the role of exopolymeric genes in modulating tomato rhizosphere microbiome assembly under a gradient of soil microbiome diversities using the B. subtilis wild-type strain UD1022 and its corresponding mutant strain UD1022eps-TasA, which is defective in exopolysaccharide (EPS) and TasA protein production.

RESULTS

qPCR revealed that the B. subtilis UD1022eps-TasA- strain has a diminished capacity to colonize tomato roots in soils with diluted microbial diversity. The analysis of bacterial β-diversity revealed significant differences in bacterial and fungal community structures following inoculation with either the wild-type or mutant B. subtilis strains. The Verrucomicrobiota, Patescibacteria, and Nitrospirota phyla were more enriched with the wild-type strain inoculation than with the mutant inoculation. Co-occurrence analysis revealed that when the mutant was inoculated in tomato, the rhizosphere microbial community exhibited a lower level of modularity, fewer nodes, and fewer communities compared to communities inoculated with wild-type B. subtilis.

CONCLUSION

This study advances our understanding of the EPS and TasA genes, which are not only important for root colonization but also play a significant role in shaping rhizosphere microbiome assembly. Future research should concentrate on specific microbiome genetic traits and their implications for rhizosphere colonization, coupled with rhizosphere microbiome modulation. These efforts will be crucial for optimizing PGPR-based approaches in agriculture.

Potential of Drought Tolerant Rhizobacteria Amended with Biochar on Growth Promotion in Wheat

Drought stress is the prime obstacle for worldwide agricultural production and necessitates innovative strategies for enhancing crop resilience. This study explores the efficacy of plant growth-promoting rhizobacteria (PGPR) and biochar (BC) as sustainable amendments for mitigating the effects of drought on wheat growth. Multiple experiments were carried out on isolated strains to assess their drought tolerance potential and multiple plant growth-promoting attributes. Experiments in the laboratory and natural environment were conducted to assess the impact of plant growth-promoting rhizobacteria, biochar, and their synergistic application on various growth parameters of wheat. The results revealed that the drought-tolerant PGPR strains (Bacillus subtilis and Bacillus tequilensis), alongside biochar (rice husk), alleviated the phytotoxic impact of drought by increasing the root length from 17.0% to 70.0% and shoot length from 30.0% to 82.0% as compared to un-inoculated stressed controls. The total chlorophyll and carotenoid contents of the plants were substantially increased to 477% and 423%, respectively, when biochar and PGPR were applied synergistically. Significant enhancements in membrane stability index, relative water content, proline, and sugar level were achieved by combining biochar and bacterial strains, resulting in increases of 19.5%, 37.9%, 219%, and 300%, respectively. The yield of wheat in terms of plant height, spike length, number of spikelets per spike, and number of grains per spike was enhanced from 26.7% to 44.6%, 23.5% to 62.7%, 91.5% to 154%, and 137% to 182%, respectively. It was concluded that the biochar-based application of PGPR induced drought tolerance in wheat under water deficit conditions, ultimately improving the production and yield of wheat.

Influence of Fertilization Methods and Types on Wheat Rhizosphere Microbiome Community and Functions

To investigate the effects of fertilization methods and types on wheat rhizosphere microorganisms, macroelement (N, K) and microelement (Zn) fertilizers were applied on wheat by foliar spraying (FS) and root irrigation (RI) methods in a field experiment. The results indicated that fertilization methods and types can have significant impacts on the diversity and structure of rhizospheric microorganisms in wheat. The application method produced more significant effects than the fertilizer type. RI-N played a more important role in improving the wheat yield and quality and affected the changes in some nitrogen-fixing bacterial communities. Finally, eight strains of bacteria belonging to Pseudomonas azotoformans and P. cedrina showed positive effects on the growth of wheat seedlings. Overall, our study provides a better understanding of the dynamics of wheat rhizosphere microbial communities and their relation to fertilization, yield, and quality, showing that plant growth-promoting rhizobacteria with nitrogen fixing may be a potential approach for more sustainable agriculture production.

Bacterial indole-3-acetic acid: A key regulator for plant growth, plant-microbe interactions, and agricultural adaptive resilience

Indole-3-acetic acid (IAA), a fundamental phytohormone categorized under auxins, not only influences plant growth and development but also plays a critical role in plant-microbe interactions. This study reviews the role of IAA in bacteria-plant communication, with a focus on its biosynthesis, regulation, and the subsequent effects on host plants. Bacteria synthesize IAA through multiple pathways, which include the indole-3-acetamide (IAM), indole-3-pyruvic acid (IPyA), and several other routes, whose full mechanisms remain to be fully elucidated. The production of bacterial IAA affects root architecture, nutrient uptake, and resistance to various abiotic stresses such as drought, salinity, and heavy metal toxicity, enhancing plant resilience and thus offering promising routes to sustainable agriculture. Bacterial IAA synthesis is regulated through complex gene networks responsive to environmental cues, impacting plant hormonal balances and symbiotic relationships. Pathogenic bacteria have adapted mechanisms to manipulate the host's IAA dynamics, influencing disease outcomes. On the other hand, beneficial bacteria utilize IAA to promote plant growth and mitigate abiotic stresses, thereby enhancing nutrient use efficiency and reducing dependency on chemical fertilizers. Advancements in analytical methods, such as liquid chromatography-tandem mass spectrometry, have improved the quantification of bacterial IAA, enabling accurate measurement and analysis. Future research focusing on molecular interactions between IAA-producing bacteria and host plants could facilitate the development of biotechnological applications that integrate beneficial bacteria to improve crop performance, which is essential for addressing the challenges posed by climate change and ensuring global food security. This integration of bacterial IAA producers into agricultural practice promises to revolutionize crop management strategies by enhancing growth, fostering resilience, and reducing environmental impact.

Progress in Microbial Fertilizer Regulation of Crop Growth and Soil Remediation Research

More food is needed to meet the demand of the global population, which is growing continuously. Chemical fertilizers have been used for a long time to increase crop yields, and may have negative effect on human health and the agricultural environment. In order to make ongoing agricultural development more sustainable, the use of chemical fertilizers will likely have to be reduced. Microbial fertilizer is a kind of nutrient-rich and environmentally friendly biological fertilizer made from plant growth-promoting bacteria (PGPR). Microbial fertilizers can regulate soil nutrient dynamics and promote soil nutrient cycling by improving soil microbial community changes. This process helps restore the soil ecosystem, which in turn promotes nutrient uptake, regulates crop growth, and enhances crop resistance to biotic and abiotic stresses. This paper reviews the classification of microbial fertilizers and their function in regulating crop growth, nitrogen fixation, phosphorus, potassium solubilization, and the production of phytohormones. We also summarize the role of PGPR in helping crops against biotic and abiotic stresses. Finally, we discuss the function and the mechanism of applying microbial fertilizers in soil remediation. This review helps us understand the research progress of microbial fertilizer and provides new perspectives regarding the future development of microbial agent in sustainable agriculture.