Production and molecular weight variation of poly-γ-glutamic acid using a recombinant Bacillus subtilis with various Pgs-component ratios

Poly-γ-glutamic acid (PGA) has been of interest as a sustainable biopolymer in industrial applications. PGA biosynthesis in Bacillus subtilis is catalyzed by a transmembrane protein complex comprising PgsB, PgsC, and PgsA. To determine the Pgs component responsible for PGA overproduction, we constructed recombinants in which the promoter of the host-derived pgs gene was replaced with another host-derived gene promoter. These recombinants were then transformed using high-copy-number plasmids with various pgs-gene combinations to enhance Pgs component in different ratios. Subsequently, PGA production was investigated in batch cultures with l-glutamate supplemented medium. The recombinant strain enhanced with pgsB alone significantly overproduced PGA (maximum production 35.8 g/L) than either the pgsC- or pgsA-enhanced strain. The molecular weight of the PGA produced with the pgsB-enhanced strain was also greater than that for the pgsC- or pgsA-enhanced strain (approximately 10-fold). Hence, PgsB enhancement alone contributes to PGA overproduction with increased molecular weight.