Antimicrobial metabolites of Bacillus velezensis FZB42 reshape rice rhizosphere microbial community composition and induce host resistance against Rhizoctonia solani

Abstract

Rhizoctonia solani, the causative agent of sheath blight disease, poses a significant threat to global rice production. Biocontrol agents (BCAs) and their metabolites offer a green and sustainable solution to emerging food production challenges, but knowledge of their role in shaping the rhizosphere microbial communities is still lacking. The current study evaluated the effect of a biocontrol bacterium Bacillus velezensis FZB42, its mutants for fengycin AK2 (ΔfenA), surfactin CH01 (ΔsrfA), and bacillomycin D AK1 (ΔbmyA) and purified metabolites fengycin (Fin), surfactin (Sin), and bacillomycin D (Bin) on induced systemic resistance in rice against Rhizoctonia solani and rhizospheric soil bacterial and fungal communities using amplicon sequencing. The FZB42 strain, its mutants, and their secondary metabolites not only induced plant resistance but also significantly inhibited the growth and disease index of R. solani. The application of FZB42 mutants enriched different bacterial phyla (Chlamydiae, Verrucomincroba, Armatimonadetes, and Candidatus saccharibacteria) and fungal phyla (Chytridiomycota, Aphleidiomycota, and Blastocladiomycota). Similarly, the application of purified metabolites also enriched various bacterial phyla (Chlamydiae, Armatimonadetes, and Planctomycetes) and fungal phyla (Basidiobolomycota, Blastocladiomycota, and Mortierellomycota). These enrichments were predominantly driven by the low and high relative abundance after treatments of FZB42, its mutants, and metabolites respectively. Our findings suggest that FZB42 and its metabolite Fin and Bin effectively reshape microbial community structures, enhance microbial network stability, and improve the resistance of rice plants against sheath blight disease. Overall, our study supports the development of biocontrol agents and utilizing antimicrobial biological resources for crop protection.