Secretion of poly-γ-glutamic acid by Bacillus atrophaeus NX-12 enhanced its root colonization and biocontrol activity
Jian Xue, Tong Tong, Rui Wang, Yibin Qiu, Yian Gu, Liang Sun, Hong Xu, Peng Lei
Abstract
Bacilli are used as biocontrol agents (BCAs) against phytopathogens and most of them can produce poly-γ-glutamic acid (γ-PGA) as one of the major extracellular polymeric substances (EPSs). However, the role of γ-PGA in plant biocontrol is still unclear. In this study, Bacillus atrophaeus NX-12 (γ-PGA yield: 16.8 g/l) was screened, which formed a strong biofilm and has been proved to be a promising BCA against Cucumber Fusarium wilt. Then, the γ-PGA synthesis gene cluster pgsBCA was knocked out by CRISPR-Cas9n. Interestingly, the antifungal ability of γ-PGA synthetase-deficient strain NX-12Δ pgs (γ-PGA yield: 1.65 g/l) was improved in vitro , while the biocontrol ability of NX-12Δ pgs was greatly diminished in situ . Data proved that γ-PGA produced by NX-12 contributes to the biofilm formation and rhizosphere colonization, which effectively improved biocontrol capability. Taken together, these findings prove that the mechanism of γ-PGA promotes the colonization of NX-12 and thus assists in controlling plant diseases, which highlight the key role of γ-PGA produced by BCA in biocontrol.