Group B Streptococcus (GBS) is a major cause of serious bacterial infection in numerous animal species. The production of capsular polysaccharide(CPs) is vital to GBS to evade host immunity. One of the genes that required for production of CPs, cpsE, has been determined to be well conserved in capsule gene cluster (cps).This study cloned the cpsE gene from Tilapia of GBS clinical isolate (serotype Ia) and expressed this gene with aid of pET-32a(+) in Escherichia coli BL21(DE3) competent cells to obtain high levels of the recombinant protein for further study about CpsE in fish and examination of its immunogenicity. The optimization of induction conditions (IPTG concentration, temperature and time) in E.coli was accomplished and let us to perform the recombinant protein induction at 37℃ for 3h,with 0.2mM IPTG in Luria Bertani (LB) medium. At the optimal conditions, recombinant protein was expressed in an insoluble form (inclusion bodies) and accounted for approximately 23% of the total protein. Purification by affinity chromatography yielded about 480mg fusion protein per liter culture.
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