Secretion of poly-?-glutamic acid by Bacillus atrophaeus NX-12 enhanced its root colonization and biocontrol activity

Bacilli are used as biocontrol agents (BCAs) against phytopathogens and most of them can produce poly-gamma-glutamic acid (gamma-PGA) as one of the major extracellular polymeric substances (EPSs). However, the role of gamma-PGA in plant biocontrol is still unclear. In this study, Bacillus atrophaeus NX-12 (gamma-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 gamma-PGA synthesis gene cluster pgsBCA was knocked out by CRISPR-Cas9n. Interestingly, the antifungal ability of gamma-PGA synthetase-deficient strain NX-12 & UDelta;pgs (gamma-PGA yield: 1.65 g/l) was improved in vitro, while the biocontrol ability of NX-12 & UDelta;pgs was greatly diminished in situ. Data proved that gamma-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 gamma-PGA promotes the colonization of NX-12 and thus assists in controlling plant diseases, which highlight the key role of gamma-PGA produced by BCA in biocontrol.

Automated summary

The study reveals that gamma-PGA promotes biofilm formation and colonization of Bacillus atrophaeus NX-12, enhancing its biocontrol capability.