Perception of Biocontrol Potential of Bacillus inaquosorum KR2-7 against Tomato Fusarium Wilt through Merging Genome Mining with Chemical Analysis

Unveiling the Biocontrol Potential of Rhizoplane Bacillus Species against Sugarcane Fusarium Wilt through Biochemical and Molecular Analysis

BACKGROUND

Biocontrol is regarded as a viable alternate technique for managing sugarcane wilt disease caused by Fusarium sacchari. Many fungal antagonists against F. sacchari, have been reported, but the potential of bacterial antagonists was explored to a limited extent, so the present study evaluated the antagonistic potential of rhizoplane Bacillus species and their mode of action.

RESULTS

A total of twenty Bacillus isolates from the rhizoplane of commercially grown sugarcane varieties were isolated. The potential isolate SRB2 had shown inhibition of 52.30, 33.33, & 44.44% and SRB20 of 35.00, 33.15, & 36.85% in direct, indirect, and remote confrontation respectively against F. sacchari. The effective strains were identified as Bacillus inaquosorum strain SRB2 and B. vallismortis strain SRB20, by PCR amplification of 16S-23S intergenic region. The biochemical studies on various direct and indirect biocontrol mechanisms revealed the production of IAA, Protease, Cellulase, Siderophores, and P solubilization. The molecular analysis revealed the presence of antimicrobial peptides biosynthetic genes like fenD (Fengycin), bmyB (Bacyllomicin) ituC (Iturin) and spaS (Subtilin) which provided a competitive edge to these isolates compared to other Bacillus strains. Under greenhouse experiments, the sett bacterization with SRB2, significantly (P < 0.001) reduced the seedling mortality by > 70% followed by SRB20 in F. sacchari inoculated pots.

CONCLUSION

The study revealed that the isolates B. inaquosorum SRB2 and B. vallismortis SRB20 can be used as potential bioagents against sugarcane Fusarium wilt.

Perception of the Biocontrol Potential and Palmitic Acid Biosynthesis Pathway of Bacillus subtilis H2 through Merging Genome Mining with Chemical Analysis

Bacillus has been widely studied for its potential to protect plants from pathogens. Here, we report the whole genome sequence of Bacillus subtilis H2, which was isolated from the tea garden soil of Guiyang Forest Park. Strain H2 showed a broad spectrum of antagonistic activities against many plant fungal pathogens and bacteria pathogens, including the rice blast fungus Magnaporthe oryzae, and showed a good field control effect against rice blast. The complete genome of B. subtilis H2 contained a 4,160,635-bp circular chromosome, with an average G + C content of 43.78%. Through the genome mining of strain H2, we identified 7 known antimicrobial compound biosynthetic gene clusters (BGCs) including sporulation killing factor, surfactin, bacillaene, fengycin, bacillibactin, subtilosin A, and bacilysin. Palmitic acid (PA), a secondary metabolite, was detected and identified in the H2 strain through genome mining analysis and gas chromatography-mass spectrometry (GC-MS). Additionally, we propose, for the first time, that the type II fatty acid synthesis (FAS) pathway in Bacillus is responsible for PA biosynthesis. This finding was confirmed by studying the antimicrobial activity of PA and conducting reverse transcription-quantitative polymerase chain reaction (RT-qPCR) experiments. We also identified numerous genes associated with plant-bacteria interactions in the H2 genome, including more than 94 colonization-related genes, more than 34 antimicrobial genes, and more than 13 plant growth-promoting genes. These findings contribute to our understanding of the biocontrol mechanisms of B. subtilis H2 and have potential applications in crop disease control.

Bacillus velezensis RC218 and emerging biocontrol agents against Fusarium graminearum and Fusarium poae in barley: in vitro, greenhouse and field conditions

Fusarium head blight (FHB) is one of the most common diseases in Argentina, affecting the quality and yield of barley grains. Fusarium graminearum sensu stricto (ss) and Fusarium poae are causal agents of FHB and potential sources of mycotoxin contamination in barley. Conventional management strategies do not lead to a complete control of FHB; therefore, biological control emerges as an eco-friendly alternative in the integrated management of the disease. In the present work, Bacillus velezensis, Bacillus inaquosorum, Bacillus nakamurai and Lactobacillus plantarum were evaluated as potential biocontrol agents against F. graminearum ss and F. poae on barley-based media. Bacillus velezensis RC218 was selected to carry out greenhouse and field trials in order to reduce FHB and mycotoxin accumulation. This strain was able to control growth of both Fusarium species and reduced deoxynivalenol (DON) and nivalenol (NIV) production by 66 % and 79 %, respectively. Bacillus inaquosorum and B. nakamurai were more effective in controlling F. poae growth, and the mean levels of reduction in DON accumulation were 50 and 38 %, and 93 and 26 % for NIV, respectively. Lactobacillus plantarum showed variable biocontrol capacity depending on the strain, with no significant mycotoxin reduction. The biocontrol on incidence and severity of FHB in the greenhouse and field trials was effective, being more efficient against F. graminearum ss and DON accumulation than against F. poae and NIV occurrence. This study provides valuable data for the development of an efficient tool based on biocontrol agents to prevent FHB-producing Fusarium species development and mycotoxin occurrence in barley, contributing to food safety.

Characterization and evaluation of Bacillus subtilis GYUN-2311 as a biocontrol agent against Colletotrichum spp. on apple and hot pepper in Korea

Crop plants are vulnerable to a variety of diseases, including anthracnose, caused by various species of Colletotrichum fungi that damages major crops, including apples and hot peppers. The use of chemical fungicides for pathogen control may lead to environmental pollution and disease resistance. Therefore, we conducted this research to develop a Bacillus subtilis-based biological control agent (BCA). B. subtilis GYUN-2311 (GYUN-2311), isolated from the rhizosphere soil of an apple orchard, exhibited antagonistic activity against a total of 12 fungal pathogens, including eight Colletotrichum species. The volatile organic compounds (VOCs) and culture filtrate (CF) from GYUN-2311 displayed antifungal activity against all 12 pathogens, with 81% control efficiency against Fusarium oxysporum for VOCs and 81.4% control efficacy against Botryosphaeria dothidea for CF. CF also inhibited germination and appressorium formation in Colletotrichum siamense and C. acutatum. The CF from GYUN-2311 showed antifungal activity against all 12 pathogens in different media, particularly in LB medium. It also exhibited plant growth-promoting (PGP) activity, lytic enzyme activity, siderophore production, and the ability to solubilize insoluble phosphate. In trials on apples and hot peppers, GYUN-2311 effectively controlled disease, with 75 and 70% control efficacies against C. siamense in wounded and unwounded apples, respectively. Similarly, the control efficacy of hot pepper against C. acutatum in wounded inoculation was 72%. Combined application of GYUN-2311 and chemical suppressed hot pepper anthracnose to a larger extent than other treatments, such as chemical control, pyraclostrobin, TK®, GYUN-2311 and cross-spraying of chemical and GYUN-2311 under field conditions. The genome analysis of GYUN-2311 identified a circular chromosome comprising 4,043 predicted protein-coding sequences (CDSs) and 4,096,969 bp. B. subtilis SRCM104005 was the strain with the highest average nucleotide identity (ANI) to GYUN-2311. AntiSMASH analysis identified secondary metabolite biosynthetic genes, such as subtilomycin, bacillaene, fengycin, bacillibactin, pulcherriminic acid, subtilosin A, and bacilysin, whereas BAGEL analysis confirmed the presence of competence (ComX). Six secondary metabolite biosynthetic genes were induced during dual culture in the presence of C. siamense. These findings demonstrate the biological control potential of GYUN-2311 against apple and hot pepper anthracnose.

Bacillus mexicanus sp. nov., a biological control bacterium isolated from the common bean (Phaseolus vulgaris L.) crop in Sinaloa, Mexico

Strain FSQ1T was isolated from the rhizosphere of the common bean (Phaseolus vulgaris L.) crop sampled in a commercial field located in the Gabriel Leyva Solano community, which belongs to the Guasave municipality (state of Sinaloa, Mexico). Based on its full-length 16S rRNA gene sequence, strain FSQ1T was assigned to the genus Bacillus (100 % similarity). This taxonomic affiliation was supported by its morphological and metabolic traits. Strain FSQ1T was a Gram-stain-positive bacterium with the following characteristics: rod-shaped cells, strictly aerobic, spore forming, catalase positive, reduced nitrate to nitrite, hydrolysed starch and casein, grew in the presence of lysozyme and 2 % NaCl, utilized citrate, grew at pH 6.0-8.0, produced acid from glucose, was unable to produce indoles from tryptophan, and presented biological control against Sclerotinia sclerotiorum. The whole-genome phylogenetic results showed that strain FSQ1T formed an individual clade in comparison with highly related Bacillus species. In addition, the maximum values for average nucleotide identity and from Genome-to-Genome Distance Calculator analysis were 91.57 and 44.20 %, respectively, with Bacillus spizizenii TU-B-10T. Analysis of its fatty acid content showed the ability of strain FSQ1T to produce fatty acids that are not present in closely related Bacillus species, such as C18 : 0 and C20 : 0. Thus, these results provide strong evidence that strain FSQ1T represents a novel species of the genus Bacillus, for which the name Bacillus mexicanus sp. nov. is proposed. The type strain is FSQ1T (CM-CNRG TB51T=LBPCV FSQ1T).

Isolation and Evaluation of the Antagonistic Activity of Cnidium officinale Rhizosphere Bacteria against Phytopathogenic fungi (Fusarium solani)

Cnidium officinale Makino, a perennial crop in the Umbeliperae family, is one of Korea's representative forest medicinal plants. However, the growing area of C. officinale has been reduced by plant disease and soil sickness caused by fusarium wilt. This study isolated rhizosphere bacteria from C. officinale, and their antagonistic activity was evaluated against Fusarium solani. Particularly, four isolated strains, namely, PT1, ST7, ST8, and SP4, showed a significant antagonistic activity against F. solani. An in planta test showed that the mortality rates of shoots were significantly low in the PT1-inoculated group. The fresh and dry weights of the inoculated plants were also higher than that of the other groups. The 16S rRNA gene sequencing identified the strain PT1 as Leclercia adecarboxylata, and downstream studies confirmed the production of antagonism-related enzymes such as siderophore and N-acetyl-β-glucosaminidase. The phosphorous solubilizing ability and secretion of related enzymes were also analyzed. The results showed that PT1 strain could be utilized as promising plant growth-promoting rhizobacteria (PGPR) and biocontrol agents (BCAs).