Contribution of Bacillomycin D in Bacillus amyloliquefaciens SQR9 to Antifungal Activity and Biofilm Formation

Bacillus amyloliquefaciens strains are capable of suppressing soilborne pathogens through the secretion of an array of lipopeptides and root colonization, and biofilm formation ability is considered a prerequisite for efficient root colonization. In this study, we report that one of the lipopeptide compounds (bacillomycin D) produced by the rhizosphere strainBacillus amyloliquefaciens SQR9 not only plays a vital role in the antagonistic activity againstFusarium oxysporum but also affects the expression of the genes involved in biofilm formation. When the bacillomycin D and fengycin synthesis pathways were individually disrupted, mutant SQR9M1, which was deficient in the production of bacillomycin D, only showed minor antagonistic activity againstF. oxysporum , but another mutant, SQR9M2, which was deficient in production of fengycin, showed antagonistic activity equivalent to that of the wild-type strain ofB. amyloliquefaciens SQR9. The results fromin vitro , rootin situ , and quantitative reverse transcription-PCR studies demonstrated that bacillomycin D contributes to the establishment of biofilms. Interestingly, the addition of bacillomycin D could significantly increase the expression levels ofkinC gene, but KinC activation is not triggered by leaking of potassium. These findings suggest that bacillomycin D contributes not only to biocontrol activity but also to biofilm formation in strainB. amyloliquefaciens SQR9.