Enhanced expression ofpgdSgene for high production of poly-γ-glutamic aicd with lower molecular weight inBacillus licheniformisWX-02

Abstract

BACKGROUND The poly-γ-glutamic acid (γ-PGA) hydrolase of PgdS affects the molecular weight and yield of γ-PGA in Bacillus subtilis, while the effects of PgdS on the γ-PGA synthesis in Bacillus licheniformis have not been investigated. RESULTS By heterologous expression in Escherichia coli, the PgdS was characterized. The purified PgdS had an optimal γ-PGA degradation activity from pH 5.5 to 6.5, with an appropriate reaction temperature from 37 °C to 45 °C. The enzyme activity could be enhanced by Zn2+, Mn2+, Ca2+ and SDS, while inhibited by Hg2+ or Cu2+. By enhanced expression of pgdS gene in vivo, the enzyme activity, protein concentration and gene transcriptional level of PgdS were improved, and γ-PGA molecular weight decreased from 1000–1200 kDa to 600–800 kDa. Moreover, the γ-PGA yield reached 20.16 g L-1, increased by 54% than the native strain (13.11 g L−1). Gene transcript levels of glutamate transporters and poly-γ-glutamate synthetase were confirmed to be improved, which might be the reason for the increased γ-PGA production. CONCLUSION Enhanced expression of pgdS gene in B. licheniformis WX-02 helped to reduce the molecular weight and improve the yield of γ-PGA. This study provided a novel strategy to regulate the molecular weight and yield of γ-PGA. © 2013 Society of Chemical Industry