Optimization of Recombinant Bacteriophage Lysin of Streptococcus Expression in Escherichia coli

To improve the expression level of bacteriophage lysin of Streptococcus (PlyC), the growth conditions of the engineering strains, that confirmed by transforming the recombinant plasmids pET-32a(+)-PlyCA and pET-32a(+)-PlyCB (PlyCA and PlyCB are two genes of PlyC) which constructed in our laboratory into E. coli BL21 (DE3) were studied. Some key parameters such as isopropyl-β-D- thiogalactopyranoside (IPTG) concentration, induction time, induction temperature and induction opportunity have been investigated to explore optimal fermentation conditions for expressing the recombinant protein. The results indicated that the best expression condition was as follows: induction started as OD600 reached about 0.3 (PlyCA) and 0.7 (PlyCB) by adding IPTG to a final concentration of 0.7mmol/L and then continued incubation for 7 h at 30°C in the 2×YT medium. The maximum yield of PlyCA and PlyCB were above 30% of the total cell proteins. This result laid the foundation for the further application study.