The extracytoplasmic sigma factor SigX supports biofilm formation and increases biocontrol efficacy in Bacillus velezensis 118

Abstract Utilizing plant growth promoting rhizobacteria (PGPR) to combat pathogens and enhance crop production is an environmentally friendly and sustainable approach. The biocontrol activity of PGPR depends on their ability to colonize plant roots and synthesize antimicrobial compounds that inhibit pathogens. However, the regulatory mechanisms underlying these processes remain unclear. In this study, we isolated and characterized Bacillus velezensis isolate 118, a soil isolate that exhibits potent biocontrol activity against Fusarium wilt of banana. Deletion of sigX, an extracytoplasmic function (ECF) sigma factor previously implicated in controlling biofilm architecture in B. subtilis, reduced biocontrol efficacy. The B. velezensis 118 sigXmutant displayed reduced biofilm formation but had only a minor defect in swarming motility and a negligible impact on lipopeptide production. These findings highlight the importance of regulatory processes important for root colonization in the effectiveness of Bacillus spp. as biocontrol agents against phytopathogens.