Characterization of a Regulator <i>pgsR</i> on Endogenous Plasmid p2Sip and Its Complementation for Poly(γ-glutamic acid) Accumulation in <i>Bacillus amyloliquefaciens</i>

<i>Bacillus amyloliquefaciens</i> NX-2S154 is a promising poly­(γ-glutamic acid) (γ-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 <i>repB</i>, <i>hsp</i>, and <i>mobB</i> and γ-PGA-synthesis regulator, <i>pgsR</i>. Elimination of p2Sip from strain NX-2S154 delayed γ-PGA secretion and decreased production of γ-PGA by 18.1%. Integration of a <i>pgsR</i> expression element into the genomic <i>Bam</i>HI locus using marker-free manipulation based on <i>pheS</i>* increased the γ-PGA titer by 8%. <i>pgsR</i> overexpression upregulated the expression of γ-PGA synthase <i>pgsB,</i> regulator <i>degQ</i>, and glutamic acid synthase <i>gltA</i>, thus increasing the γ-PGA production in <i>B. amyloliquefaciens</i> NB. Our results indicated that <i>pgsR</i> from p2Sip plays an important regulatory role in γ-PGA synthesis in <i>B. amyloliquefacien</i>s.