Construction of a mutant Bacillus subtilis strain for high purity poly-γ-glutamic acid production

Objective To construct a Bacillus subtilis strain for improved purity of poly-γ-glutamic acid. Results The construction of strain GH16 was achieved by knocking out five genes encoding extracellular proteins and an operon from Bacillus subtilis G423. We then analyzed the amount of protein impurities in the γ-PGA produced by the resulting strain GH16/pHPG, which decreased from 1.48 to 1.39%. Subsequently the fla-che operon, PBSX , as well as the yrpD , ywoF and yclQ genes were knocked out successively, resulting in the mutant strains GH17, GH18 and GH19. Ultimately, the amount of protein impurities was reduced from 1.48 to 0.83%. In addition, the amount of polysaccharide impurities in the γ-PGA was also decreased from 2.21 to 1.93% after knocking out the epsA-O operon. Conclusions The high purity γ-PGA producer was constructed, and the resulting strain was a promising platform for the manufacture of other highly pure extracellular products and secretory proteins.