Characterization of a Bacillus velezensis strain isolated from Bolbostemmatis Rhizoma displaying strong antagonistic activities against a variety of rice pathogens

Characterization of Bacillus velezensis TJS119 and its biocontrol potential against insect pathogens

Introduction

The white-spotted flower chafer (Protaetia brevitarsis seulensis), which is widely distributed in Asian countries, is traditionally used in oriental medicine. However, its larvae are prone to severe damage by green muscardine disease (caused by Metarhizium anisopliae) during breeding. The aim of this study was to characterize Bacillus velezensis TJS119, which has been isolated from freshwater, and investigate its potential as a biocontrol agent against M. anisopliae in insects.

Methods

TJS119 was obtained from freshwater samples in the Republic of Korea and was classified as B. velezensis. We evaluated its in vitro antifungal effect, sequenced the bacterial whole genome, mined genes responsible for the synthesis of secondary metabolites, performed secondary metabolite analysis Ultra performance liquid chromatography-mass spectrometry (UPLC-MS/MS), and conducted bioassays for determining green muscardine disease control ability.

Results

Bacillus velezensis TJS119 inhibited the mycelial growth of M. anisopliae in vitro. The size of the B. velezensis TJS119 genome was estimated to be 3,890,913 bp with a GC content of 46.67% and 3,750 coding sequences. Biosynthetic gene clusters for secondary metabolites with antifungal activity were identified in the genome. Lipopeptides, including fengycin secreted by TJS119 exhibit antifungal activity. Application of TJS119 for the biocontrol against green muscardine disease increased the viability of white-spotted flower chafer by 94.7% compared to the control.

Discussion

These results indicate that B. velezensis TJS119 is a potential biocontrol agent for insect pathogens.

Evaluation of the control efficacy of antagonistic bacteria from V-Ti magnetite mine tailings on kiwifruit brown spots in pot and field experiments

Seemingly barren heavy-metal-polluted vanadium (V) and titanium (Ti) magnetite mine tailings contain various functional microbes, yet it is unclear whether this includes microbial resources relevant to the biological control of plant diseases. Kiwifruit brown leaf spot disease, caused by Corynespora cassiicola, can seriously reduce kiwifruit yield. To discover effective control measures for kiwifruit leaf spot, 18 bacteria strains among 136 tailing-isolated bacteria from V-Ti magnetite mine tailings were identified as inhibiting C. cassiicola by the confrontation plate method, indicating that antagonistic bacteria surviving in the V-Ti magnetite mine tailings were present at a low level. The 18 antagonistic strains could be divided into two BOX-A1R clusters. The 13 representative strains that were selected for phylogenetic tree construction based on their 16S rRNA sequences belonged to the Bacillus genus. Five predominant strains exhibited different toxin-production times and intensities, with four of them initiating toxin production at 32 h. Among them, Bacillus sp. KT-10 displayed the highest bacteriostatic rate (100%), with a 37.5% growth inhibition rate and an antagonistic band of 3.2 cm against C. cassiicola. Bacillus sp. KT10 also showed a significant inhibitory effect against the expansion speed of kiwifruit brown spots in the pot. The relative control effect was 78.48 and 83.89% at 7 days after the first and last spraying of KT-10 dilution, respectively, confirming a good effect of KT-10 on kiwifruit brown leaf spots in the field. This study demonstrated for the first time that there are some antagonistic bacteria to pathogenic C. cassiicola in V-Ti magnetite mine tailings, and Bacillus sp. KT10 was found to have a good control effect on kiwifruit brown leaf spots in pots and fields, which provided an effective biological control measurement for kiwifruit brown leaf spots.

Biocontrol manufacturing and agricultural applications of Bacillus velezensis

Many microorganisms have been reported as bioagents for producing ecofriendly, cost-effective, and safe products. Some Bacillus species of bacteria can be used in agricultural applications. Bacillus velezensis in particular has shown promising results for controlling destructive phytopathogens and in biofungicide manufacturing. Some B. velezensis strains can promote plant growth and display antibiotic activities against plant pathogen agents. In this review, we focus on the often-overlooked potential properties of B. velezensis as a bioagent for applications that will extend beyond the traditional agricultural uses. We delve into its versatility and future prospects, the challenges such uses may encounter, and some drawbacks associated with B. velezensis-based products.

Whole-genome analysis revealed the growth-promoting and biological control mechanism of the endophytic bacterial strain Bacillus halotolerans Q2H2, with strong antagonistic activity in potato plants

Introduction

Endophytes are colonizers of healthy plants and they normally exhibit biocontrol activities, such as reducing the occurrence of plant diseases and promoting plant growth. The endophytic bacterium Bacillus halotolerans Q2H2 (Q2H2) was isolated from the roots of potato plants and was found to have an antagonistic effect on pathogenic fungi.

Methods

Q2H2 was identified by morphological observations, physiological and biochemical identification, and 16S rRNA gene sequence analysis. Genes related to the anti-fungal and growth-promoting effects were analyzed using whole-genome sequencing and comparative genomic analysis. Finally, we analyzed the growth-promoting and biocontrol activities of Q2H2 in potato plants using pot experiments.

Results

Antagonism and non-volatile substance plate tests showed that Q2H2 had strong antagonism against Fusarium oxysporum, Fusarium commune, Fusarium graminearum, Fusarium brachygibbosum, Rhizoctonia solani and Stemphylium solani. The plate test showed that Q2H2 had the ability to produce proteases, cellulases, β-1,3-glucanase, dissolved organic phosphate, siderophores, indole-3-acetic acid (IAA), ammonia and fix nitrogen. The suitable growth ranges of Q2H2 under different forms of abiotic stress were pH 5-9, a temperature of 15-30°C, and a salt concentration of 1-5%. Though whole-genome sequencing, we obtained sequencing data of approximately 4.16 MB encompassed 4,102 coding sequences. We predicted 10 secondary metabolite gene clusters related to antagonism and growth promotion, including five known products surfactin, bacillaene, fengycin, bacilysin, bacillibactin, and subtilosin A. Average nucleotide identity and comparative genomic analyses revealed that Q2H2 was Bacillus halotolerans. Through gene function annotation, we analyzed genes related to antagonism and plant growth promotion in the Q2H2 genome. These included genes involved in phosphate metabolism (pstB, pstA, pstC, and pstS), nitrogen fixation (nifS, nifU, salA, and sufU), ammonia production (gudB, rocG, nasD, and nasE), siderophore production (fhuC, fhuG, fhuB, and fhuD), IAA production (trpABFCDE), biofilm formation (tasA, bslA, and bslB), and volatile compound production (alsD, ilvABCDEHKY, metH, and ispE), and genes encoding hydrolases (eglS, amyE, gmuD, ganB, sleL, and ydhD). The potato pot test showed that Q2H2 had an obvious growth-promoting effect on potato roots and better control of Fusarium wilt than carbendazim.

Conclusion

These findings suggest that the strain-specific genes identified in bacterial endophytes may reveal important antagonistic and plant growth-promoting mechanisms.

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.

Biocontrol ability of Bacillus velezensis T9 against Apiospora arundinis causing Apiospora mold on sugarcane

Sugarcane (Saccharum officinarum L.) may be infected with Apiospora, which can produce the toxin 3-nitropropionic acid (3-NPA) during improper transportation and storage. The consumption of sugarcane that contains 3-NPA can lead to food poisoning. Therefore, this study sought to explore a novel biocontrol agent to prevent and control Apiospora mold. Bacteria were isolated from the soil of healthy sugarcane and identified as Bacillus velezensis T9 through colony morphological, physiological and biochemical characterization and molecular identification. The inhibitory effect of B. velezensis T9 on Apiospora mold on sugarcane was analyzed. Assays of the cell suspension of strain T9 and its cell-free supernatant showed that T9 had significant in vitro antifungal activities against Apiospora arundinis and thus, would be a likely antagonist. Scanning electron microscopy and transmission electron microscopy showed that treatment with T9 significantly distorted the A. arundinis mycelia, perforated the membrane, contracted the vesicles, and decomposed most organelles into irregular fragments. A re-isolation experiment demonstrates the ability of T9 to colonize the sugarcane stems and survive in them. This strain can produce volatile organic compounds (VOCs) that are remarkably strong inhibitors, and it can also form biofilms. Additionally, the cell-free supernatant significantly reduced the ability of A. arundinis to produce 3-NPA and completely inhibited its production at 10%. Therefore, strain T9 is effective at controlling A. arundinis and has the potential for further development as a fungal prevention agent for agricultural products.

Screening and characterization of biocontrol bacteria isolated from Ageratum conyzoides against Collectotrichum fructicola causing Chinese plum (Prunus salicina Lindl.) anthracnose

Chinese plum (Prunus salicina Lindl.) is a nutritionally and economically important stone fruit widely grown around the world. Anthracnose, caused by Collectotrichum spp., is one of the primary biotic stress factors limiting plum production. Medicinal plants may harbor rhizospheric or endophytic microorganisms that produce bioactive metabolites that can be used as anthracnose biocontrol agents. Here, 27 bacterial isolates from the medicinal plant A. conyzoides with diverse antagonistic activities against C. fructicola were screened. Based on morphological, physiological, biochemical, and molecular characterization, 25 of these isolates belong to different species of genus Bacillus, one to Pseudomonas monsensis, and one more to Microbacterium phyllosphaerae. Eight representative strains showed high biocontrol efficacy against plum anthracnose in a pot experiment. In addition, several Bacillus isolates showed a broad spectrum of inhibitory activity against a variety of fungal phytopathogens. Analysis of the volatile organic compound profile of these eight representative strains revealed a total of 47 compounds, most of which were ketones, while the others included alkanes, alkenes, alcohols, pyrazines, and phenols. Overall, this study confirmed the potential value of eight bacterial isolates for development as anthracnose biocontrol agents.

Bacillus velezensis BV01 Has Broad-Spectrum Biocontrol Potential and the Ability to Promote Plant Growth

To evaluate the potential of a bacterial strain as a fungal disease control agent and plant growth promoter, its inhibitory effects on phytopathogens such as Bipolaris sorokiniana, Botrytis cinerea, Colletotrichum capsici, Fusarium graminearum, F. oxysporum, Neocosmospora rubicola, Rhizoctonia solani, and Verticillium dahliae were investigated. The results showed that the inhibitory rates in dual-culture and sterile filtrate assays against these eight phytopathogens ranged from 57% to 83% and from 36% to 92%. The strain was identified as Bacillus velezensis based on morphological and physiological characterization as well as phylogenetic analyses of 16S rRNA and the gyrase subunit A protein (gyrA) regions. The results demonstrated that B. velezensis was able to produce fungal cell-wall-degrading enzymes, namely, protease, cellulase, and β-1,3-glucanase, and the growth-promotion substances indole-3-acetic acid (IAA) and siderophore. Furthermore, B. velezensis BV01 had significant control effects on wheat root rot and pepper Fusarium wilt in a greenhouse. Potted growth-promotion experiments displayed that BV01 significantly increased the height, stem diameter, and aboveground fresh and dry weights of wheat and pepper. The results imply that B. velezensis BV01, a broad-spectrum biocontrol bacterium, is worth further investigation regarding its practical applications in agriculture.