Marker assisted detection and LC-MS analysis of antimicrobial compounds in different Bacillus strains and their antifungal effect on Sclerotinia sclerotiorum

Bacillus strains are well studied for antagonistic effect against fungal pathogens, but the selection of potential antifungal strains is laborious and time-consuming process. Newly developed genetic markers and LC-MS based detection was undertaken simultaneously to detect eight antimicrobial compounds viz., surfactin, bacillomycin, iturin, fengycin/plipastatin, bacilysin, bacillaene, bacillibactin and plantazolicin in forty-seven Bacillus strains. Out of these strains, 19 were positive for the presence of marker genes encoding antimicrobial compounds. Bacillus strains FZB42, EZ1509, EZ1507, VM10, GBAC46, VM49 and LLCG43 possessed genes for maximum number of antimicrobial compounds. LC-MS analysis of antimicrobial compounds showed corresponding results except OKB105 and 168. Contrary to marker-based detection of genes, LC-MS analysis revealed that OKB105 can produce surfactin but unable to synthesize fengycin, while 168 was deficit in both compounds. To assay antifungal potential, 19 Bacillus strains and their methanolic extracts were tested in vitro to inhibit mycelial growth of S. sclerotiorum. Results revealed that EZ1509, VM10, GBAC46, VM49 and FZB42 showed highest inhibitory activity. A bioassay on detached rapeseed leaves demonstrated that strains VM10, EZ1509, FZB42 and GBAC46 were excellent in reducing lesion diameter, while, OKB105 and 168 were completely ineffective to control S. sclerotiorum. Interestingly, antifungal activity of Bacillus strains was positively co-related to the number of antimicrobial genes, indicating their role in antifungal activity of Bacillus strains. Our findings suggest that combining genetic markers and LC-MS analysis can rapidly screen Potential Bacillus strains with antifungal attributes and this screening method can serve as foundation for the development of new biopesticides.