Effect of volatile compounds produced by the cotton endophytic bacterial strain Bacillus sp. T6 against Verticillium wilt

Unlocking Rhizosphere Dynamics: Exploring Mechanisms of Plant-Microbe Interactions for Enhanced Tea (Camellia sinensis (L.) O. Kuntze) Productivity

The rhizosphere, the interface between plant roots and soil, refers to the contact zone where plants and soil microbes engage in beneficial and parasitic interactions. The significant interactions and their importance form a dynamic interface between the roots of plants and the soil. Beneficial ones, especially plant growth-promoting bacteria (PGPB) and arbuscular mycorrhizal fungi (AMF), improve plant development and enhance stress resistance due to microbial secretions, exudates from roots, and edaphic factors. All these are very important in cultivating tea (Camellia sinensis (L.) O Kuntze) plants, boosting growth, yield, and leaf content of amino acids, proteins, caffeine, and polyphenols. Yet, the molecular mechanisms of such interactions necessitate high-end technologies like genome editing and proteomics to fine-tune rhizosphere dynamics for greater plant health and productivity. The root exudates, rich in nutrients, serve as a source of food for the soil microbes while facilitating communication and colonisation by beneficial organisms, such as AMF and bacteria, thus significantly impacting the performance of a tea plant. High nitrogen fertilisers are readily applied in tea farming, although environmental risks include soil acidification and increased emissions of nitrous oxide (N2O), a potent greenhouse gas. Understanding and manipulating plant root-soil microbe interactions are critical for developing sustainable farming systems that enhance productivity without causing environmental damage. This review describes the mechanisms by which beneficial microbes function in the rhizosphere, strategies for modifying root exudates to improve tea production, and the tea microbiome's underexplored potential in contributing towards sustainability. This review thus emerges as one that presents knowledge gaps and possible future directions in tea microbiome science predicated on the amelioration of tea farming by enhancing productivity and ensuring environmental sustainability.

Unlocking the potential of ecofriendly guardians for biological control of plant diseases, crop protection and production in sustainable agriculture

Several beneficial microbial strains inhibit the growth of different phytopathogens and commercialized worldwide as biocontrol agents (BCAs) for plant disease management. These BCAs employ different strategies for growth inhibition of pathogens, which includes production of antibiotics, siderophores, lytic enzymes, bacteriocins, hydrogen cyanide, volatile organic compounds, biosurfactants and induction of systemic resistance. The efficacy of antagonistic strains could be further improved through genetic engineering for better disease suppression in sustainable farming practices. Some antagonistic microbial strains also possess plant-growth-promoting activities and their inoculation improved plant growth in addition to disease suppression. This review discusses the characterization of antagonistic microbes and their antimicrobial metabolites, and the application of these BCAs for disease control. The present review also provides a comprehensive summary of the genetic organization and regulation of the biosynthesis of different antimicrobial metabolites in antagonistic strains. Use of molecular engineering to improve production of metabolites in BCAs and their efficacy in disease control is also discussed. The application of these biopesticides will reduce use of conventional pesticides in disease control and help in achieving sustainable and eco-friendly agricultural systems.

Inhibition of Xanthomonas growth by bioactive volatiles from Pseudomonas sp. triggers remarkable changes in the phytopathogen transcriptome

Volatile organic compounds (VOCs) produced by microorganisms may have a noteworthy role in the control of plant pathogens. Xanthomonas are a well-studied group of phytobacteria that cause diverse diseases in economically important crops worldwide. Key species that infect sugarcane are X. albilineans (Xab) and X. axonopodis pv. vasculorum (Xav). Here, we investigated VOC-producing bacteria with antagonistic effects against Xab and Xav. We demonstrated that VOCs produced by Pseudomonas sp. V5-S-D11 was able to abolish the growth of these pathogens. A set of 32 VOCs was identified in the volatilome of V5-S-D11, with 10 showing a concentration-dependent inhibitory effect on both phytobacteria. Among them, dimethyl disulfide (DMDS), a volatile sulfur compound, has the potential to be biotechnologically explored in agriculture since it can improve plant growth and induce systemic resistance against plant pathogens. Interestingly, transcriptomic analysis of Xab treated with DMDS revealed several up-regulated metabolic pathways such as a two-component system, flagellar assembly, chemotaxis, and a bacterial secretion system. Although the ethanol (ETOH) used as DMDS solvent did not inhibit Xab growth, it triggered a similar up-regulation of some genes, indicating that this phytopathogen can deal with ETOH better than DMDS. Overall, this study explores the wide role of VOCs in the interactions with bacteria. Moreover, our results indicate that VOCs from Pseudomonas sp. may represent a novel biotechnological strategy to counteract diseases caused by Xanthomonas species and can be further exploited for sustainable approaches in agriculture.

Delineating the soil physicochemical and microbiological factors conferring disease suppression in organic farms

Organic farming utilizes farmyard manure, compost, and organic wastes as sources of nutrients and organic matter. Soil under organic farming exhibits increased microbial diversity, and thus, becomes naturally suppressive to the development of soil-borne pathogens due to the latter's competition with resident microbial communities. Such soils that exhibit resistance to soil-borne phytopathogens are called disease-suppressive soils. Based on the phytopathogen suppression range, soil disease suppressiveness is categorised as specific- or general- disease suppression. Disease suppressiveness can either occur naturally or can be induced by manipulating soil properties, including the microbiome responsible for conferring protection against soil-borne pathogens. While the induction of general disease suppression in agricultural soils is important for limiting pathogenic attacks on crops, the factors responsible for the phenomenon are yet to be identified. Limited efforts have been made to understand the systemic mechanisms involved in developing disease suppression in organically farmed soils. Identifying the critical factors could be useful for inducing disease suppressiveness in conducive soils as a cost-effective alternative to the application of pesticides and fungicides. Therefore, this review examines the soil properties, including microbiota, and assesses indicators related to disease suppression, for the process to be employed as a tactical option to reduce pesticide use in agriculture.

Exploring the Potential of Bacterial Endophytes in Plant Disease Management

Endophytic bacteria live in the internal tissues of plants, forming symbiotic, mutualistic, commensalistic and trophobiotic relationships. Some are spread via seeds after sprouting from the rhizosphere or phyllosphere. These bacteria capable of promoting plant growth and impart biotic stress by synthesing plant growth hormones, ACC deaminase, organic acids and siderophore. Endophytes aid in phytoremediation by removing soil contaminants and boosting soil fertility via phosphate solubilization and nitrogen fixation. The endophytic microbes are becoming increasingly popular in biotechnological applications which supports sustainable growth of non-food crops for biomass and biofuel. They offer valuable natural materials which is used in medicine, agriculture and industry. Bacterial endophytes are endowed with the enormous potential in the biological treatment of plant pathogens and considered as the superior alternative to synthetic fungicides. The review emphasizes benefits of bacterial endophytes in promoting plant growth and prospects of agricultural applications viz., increasing crop yield under biotic stress condition and their mode of action towards plant diseases. It also summarises the diverse and vital role of endophytes in agroecosystems as well as insights for sustainable agriculture and crop resilience.

Analysis of Bioactive Compounds Produced by Bacillus mojavensis ZA1 and Their Antagonistic Effect on Colletotrichum coccodes by GC-MS

The plant disease Colletotrichum coccodes, which lowers potato yields, poses a severe danger to the booming potato industry. Isolated plant endophytic bacteria from highland pasture can produce a variety of metabolites that lessen the risk that the pathogen C. coccodes poses to plant growth and development. Therefore, the objective of our work was to assess substances with antipathogenic properties made by the endophytic bacteria Bacillus mojavensis ZA1. Gas chromatography-mass spectrometry (GC-MS) was used in our investigation to accomplish a thorough structural elucidation of the antipathogenic compounds produced by the endophytic bacterial strain B. mojavensis ZA1. The results showed that the metabolites extracted from ethyl acetate as an extractant were the most effective in inhibiting the pathogen C. coccodes, with 60.95% inhibition. Thirty-five distinct chemicals, including acids, esters, ketones, alcohols, amino acid ammonium salts, cyclic ethers, aromatic hydrocarbons, and heterocyclic compounds, were among the metabolites that may inhibit C. coccodes. Further analysis of the chemical groups in the compound structures revealed the potential of driving groups, such as hydroxyl, carbonyl, ester, benzene, carbon-carbon double bonds, and carbon rings, that prevent C. coccodes from performing its function. This study opens up new opportunities for plant protection programs by demonstrating that natural chemicals produced by B. mojavensis ZA1 can be used as candidates for cutting-edge plant disease management treatments.

The novel bacteriocin BacYB1 produced by Leuconostoc mesenteroides YB1: From recent analytical characterization to biocontrol Verticillium dahliae and Agrobacterium tumefaciens

Biocontrol of phytopathogens involving the use of bioactive compounds produced by lactic acid bacteria (LAB), is a promising approach to manage many diseases in agriculture. In this study, a lactic acid bacterium designated YB1 was isolated from fermented olives and selected for its antagonistic activity against Verticillium dahliae (V. dahliae) and Agrobacterium tumefaciens (A. tumefaciens). Based on the 16S rRNA gene nucleotide sequence analysis (1565 pb, accession number: OR714267), the new isolate YB1 bacterium was assigned as Leuconostoc mesenteroides YB1 (OR714267) strain. This bacterium produces an active peptide "bacteriocin" called BacYB1, which was purified in four steps. Matrix-assisted lasers desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) based approach was performed to identify and characterize BacYB1. The exact mass was 5470.75 Da, and the analysis of the N-terminal sequence (VTRASGASTPPGTASPFKTL) of BacYB1 revealed no significant similarity to currently available antimicrobial peptides. The BacYB1 displayed a bactericidal mode of action against A. tumefaciens. The potentiel role of BacYB1 to supress the growth of A. tumefaciens was confirmed by live-dead cells viability assay. In pot experiments, the biocontrol efficacy of BacYB1 against V. dahliae wilt on young olive trees was studied. The percentage of dead plants (PDP) and the final mean symptomes severity (FMS) of plants articifialy infected by V. dahliae and treated with the pre-purified peptide BacYB1 (preventive and curative treatments) were significantly inferior to untreated plants. Biochemical analysis of leaves of the plants has shown that polyophenols contents were highly detected in plants infected by V. dahliae and the highest contents of chlorophyl a, b and total chlorophyll were recorded in plants treated with the combination of BacYB1 with the biofertilisant Humivital. BacYB1 presents a promising alternative for the control of Verticillium wilt and crown gall diseases.

Insights into the biocontrol and plant growth promotion functions of Bacillus altitudinis strain KRS010 against Verticillium dahliae

BACKGROUND

Verticillium wilt, caused by the fungus Verticillium dahliae, is a soil-borne vascular fungal disease, which has caused great losses to cotton yield and quality worldwide. The strain KRS010 was isolated from the seed of Verticillium wilt-resistant Gossypium hirsutum cultivar "Zhongzhimian No. 2."

RESULTS

The strain KRS010 has a broad-spectrum antifungal activity to various pathogenic fungi as Verticillium dahliae, Botrytis cinerea, Fusarium spp., Colletotrichum spp., and Magnaporthe oryzae, of which the inhibition rate of V. dahliae mycelial growth was 73.97% and 84.39% respectively through confrontation test and volatile organic compounds (VOCs) treatments. The strain was identified as Bacillus altitudinis by phylogenetic analysis based on complete genome sequences, and the strain physio-biochemical characteristics were detected, including growth-promoting ability and active enzymes. Moreover, the control efficiency of KRS010 against Verticillium wilt of cotton was 93.59%. After treatment with KRS010 culture, the biomass of V. dahliae was reduced. The biomass of V. dahliae in the control group (Vd991 alone) was 30.76-folds higher than that in the treatment group (KRS010+Vd991). From a molecular biological aspect, KRS010 could trigger plant immunity by inducing systemic resistance (ISR) activated by salicylic acid (SA) and jasmonic acid (JA) signaling pathways. Its extracellular metabolites and VOCs inhibited the melanin biosynthesis of V. dahliae. In addition, KRS010 had been characterized as the ability to promote plant growth.

CONCLUSIONS

This study indicated that B. altitudinis KRS010 is a beneficial microbe with a potential for controlling Verticillium wilt of cotton, as well as promoting plant growth.

Optimization of the fermentation media and growth conditions of Bacillus velezensis BHZ-29 using a Plackett-Burman design experiment combined with response surface methodology

Introduction

Bacillus velezensis occurs extensively in the soil environment. It produces a range of antimicrobial compounds that play an important role in the field of biological control. However, during the actual application process it is often affected by factors such as the medium formulation and fermentation conditions, and therefore biocontrol measures often do not achieve their expected outcomes.

Methods

In this study, the B. velezensis BHZ-29 strain was used as the research object. The carbon and nitrogen sources, and inorganic salts that affect the number of viable bacteria and antibacterial potency of B. velezensis BHZ-29, were screened by a single factor test. A Plackett-Burman design experiment was conducted to determine the significant factors affecting the number of viable bacteria and antibacterial potency, and a Box-Behnken design experiment was used to obtain the optimal growth of B. velezensis BHZ-29. The medium formula that produced the highest number of viable bacteria and most antibacterial substances was determined. The initial pH, temperature, amount of inoculant, liquid volume, shaking speed, and culture time were determined by a single factor test. The factors that had a significant influence on the number of viable bacteria of B. velezensis BHZ-29 were selected by an orthogonal test. A Box-Behnken design experiment was conducted to obtain the optimal fermentation conditions, and highest number of viable bacteria and antibacterial titer.

Results

Molasses, peptone, and magnesium sulfate had significant effects on the viable count and antibacterial titer of B. velezensis BHZ-29. The viable count of B. velezensis BHZ-29 increased from 7.83 × 109 to 2.17 × 1010 CFU/mL, and the antibacterial titer increased from 111.67 to 153.13 mm/mL when the optimal media were used. The optimal fermentation conditions for B. velezensis BHZ-29 were as follows: temperature 25.57°C, pH 7.23, culture time 95.90 h, rotation speed 160 rpm, amount of inoculant 2%, and liquid volume 100 ml. After the optimization of fermentation conditions, the number of viable bacteria increased to 3.39 × 1010 CFU/mL, and the bacteriostatic titer increased to 158.85 mm/ml.The plant height and leaf number of cotton plants treated with BHZ-29 fermentation broth were higher than those of cotton inoculated with Verticillium dahliae. The number of bacteria was 1.15 × 107 CFU/g, and the number of fungi was 1.60 × 105 spores/g. The disease index of the cotton seedlings treated with the optimized fermentation broth was 2.2, and a control effect of 93.8% was achieved. B. velezensis BHZ-29 could reduce the disease index of cotton Verticillium wilt and had a controlling effect on the disease. The best effect was achieved in the treatment group with an inoculation concentration of 2 × 108 CFU/ml, the disease index was 14.50, and a control effect of 84.18% was achieved.

Discussion

The fermentation process parameters of the number of viable bacteria and antibacterial titer by strain B. velezensis BHZ-29 were optimized to lay a foundation for the practical production and application of strain B. velezensis BHZ-29 in agriculture.

Characterization of the Endophytic Bacillus subtilis KRS015 Strain for Its Biocontrol Efficacy Against Verticillium dahliae

Endophytes play important roles in promoting plant growth and controlling plant diseases. Verticillium wilt is a vascular wilt disease caused by Verticillium dahliae, a widely distributed soilborne pathogen that causes significant economic losses on cotton each year. In this study, an endophyte KRS015, isolated from the seed of the Verticillium wilt-resistant Gossypium hirsutum 'Zhongzhimian No. 2', was identified as Bacillus subtilis by morphological, phylogenetic, physiological, and biochemical analyses. The volatile organic compounds (VOCs) produced by KRS015 or its cell-free fermentation extract had significant antagonistic effects on various pathogenic fungi, including V. dahliae. KRS015 reduced Verticillium wilt index and colonization of V. dahliae in treated cotton seedlings significantly; the disease reduction rate was ∼62%. KRS015 also promoted plant growth, potentially mediated by the growth-related cotton genes GhACL5 and GhCPD-3. The cell-free fermentation extract of KRS015 triggered a hypersensitivity response, including reactive oxygen species (ROS) and expression of resistance-related plant genes. VOCs from KRS015 also inhibited germination of conidia and the mycelial growth of V. dahliae, and were mediated by growth and development-related genes such as VdHapX, VdMcm1, Vdpf, and Vel1. These results suggest that KRS015 is a potential agent for controlling Verticillium wilt and promoting growth of cotton.

Endophytes Modulate Plant Genes: Present Status and Future Perspectives

Interactions among endophytes and plants are widespread and can vary from neutral or positive or negative. Plants are continually in a functionally dynamic state due to interactions with diverse endophytic microorganisms, which produce various metabolic substances. Through quorum sensing, these substances not only help endophytes to outcompete other host-associated pathogens or microbes but also allow them to overcome the plant immune system. Manifold interactions between endophytic microbiota cause a reflective impact on the host plant functioning and the development of 'endobiomes,' by synthesizing chemicals that fill the gap between host and endophytes. Despite the advances in the field, specific mechanisms for the endophytes' precise methods to modulate plant genome and their effects on host plants remain poorly understood. Deeper genomic exploration can provide a locked away understanding of the competencies of endophytes and their conceivable function in host growth and health. Endophytes also can modify host metabolites, which could manipulate plants' growth, adaptation, and proliferation, and can be a more exciting and puzzling topic that must be properly investigated. The consequence of the interaction of endophytes on the host genome was analyzed as it can help unravel the gray areas of endophytes about which very little or no knowledge exists. This review discusses the recent advances in understanding the future challenges in the emerging research investigating how endosymbionts affect the host's metabolism and gene expression as an effective strategy for imparting resistance to biotic and abiotic challenges.

Efficacy of Seed-Biopriming with Trichoderma spp. and Foliar Spraying of ZnO-Nanoparticles Induce Cherry Tomato Growth and Resistance to Fusarium Wilt Disease

Several microbes that cause plant diseases drastically lower the production of agriculture and jeopardize the safety of the world's food supply. As a result, sustainable agriculture requires disease management tactics based on modern, eco-friendly techniques as alternatives to various agrochemicals. The current study aimed to assess the antifungal activity of ZnO-nanoparticles against Fusarium solani in-vitro, and the ability of two antagonistic Trichoderma isolates, Trichoderma viride and Trichoderma harzianum, to produce antifungal secondary metabolites and identify them using gas chromatography-mass spectrometry, and to evaluate the combined effects of foliar spray of ZnO-nanoparticles and bioprimed seeds of cherry tomato (Solanum lycopersicum L.) with two antagonistic Trichoderma isolates against Fusarium wilt disease caused by Fusarium solani in greenhouse conditions. The results revealed that, in-vitro, the highest concentration of ZnO nanoparticles (3000 ppm) resulted in the greatest decrease in Fusarium solani mycelial growth (90.91% inhibition). The scanning electron microscopy demonstrated the evident distortion in Fusarium solani growing mycelia treated with ZnO-nanoparticles, which might be the source of growth suppression. Additionally, twenty-eight bioactive chemical compounds were isolated and identified from Trichoderma spp. ethyl acetate crude extracts using gas chromatography-mass spectrometry. In a greenhouse experiment, the combination of bioprimed cherry tomato plants with Trichoderma harzianum and foliar spraying of ZnO-nanoparticles at 3000 ppm was the most effective interaction treatment for reducing disease severity index (23.4%) and improving the vegetative growth parameters, micronutrient contents (Mn, Zn, and Fe in leaves), and chlorophyll content (SPAD unit), as well as stimulating phenylalanine ammonia-lyase activity of cherry tomato leaves at 75 days after sowing. In conclusion, the antifungal potential of seed-biopriming with antagonistic Trichoderma isolates and the foliar spraying of ZnO-nanoparticles can boost cherry tomato growth and confer resistance to Fusarium wilt caused by Fusarium solani.

Bacillus VOCs in the Context of Biological Control

A contemporary agricultural production system relying on heavy usage of agrochemicals represents a questionable outlook for sustainable food supply in the future. The visible negative environmental impacts and unforeseen consequences to human and animal health have been requiring a shift towards the novel eco-friendly alternatives for chemical pesticides for a while now. Microbial-based biocontrol agents have shown a promising potential for plant disease management. The bacteria of the genus Bacillus have been among the most exploited microbial active components due to several highly efficient mechanisms of action against plant pathogens, as well as a palette of additional plant-beneficial mechanisms, together with their suitable properties for microbial biopesticide formulations. Among other bioactive metabolites, volatile organic compounds (VOCs) have been investigated for their biocontrol applications, exhibiting the main advantage of long-distance effect without the necessity for direct contact with plants or pathogens. The aim of this study is to give an overview of the state-of-the-art in the field of Bacillus-based VOCs, especially in terms of their antibacterial, antifungal, and nematicidal action as the main segments determining their potential for biocontrol applications in sustainable agriculture.