Characterization of a regulator pgsR on endogenous plasmid p2Sip and its complementation for poly-(γ-glutamic acid) accumulation in Bacillus amyloliquefaciens.

Bacillus amyloliquefaciens NX-2S154 is a promising poly(gamma-glutamic acid) (gamma-PGA) producing strain discovered in previous studies. However, the wild-type strain contains an unknown endogenous plasmid, p2Sip, which causes low transformation efficiency and instability of exogenous plasmids. In our study, p2Sip is 5622 bp with 41% G+C content and contains four putative open reading frames (ORFs), including genes repB, hsp, and mobB and gamma-PGA-synthesis regulator, pgsR. Elimination of p2Sip from strain NX-2S154 delayed gamma-PGA secretion and decreased production of gamma-PGA by 18.1%. Integration of a pgsR expression element into the genomic BamHI locus using marker-free manipulation based on pheS* increased the gamma-PGA titer by 8%. pgsR overexpression upregulated the expression of gamma-PGA synthase pgsB, regulator degQ, and glutamic acid synthase gltA, thus increasing the gamma-PGA production in B. amyloliquefaciens NB. Our results indicated that pgsR from p2Sip plays an important regulatory role in gamma-PGA synthesis in B. amyloliquefaciens.