Expression of Hblys in the E. coli High Cell Density Culture Using Lactose as an Inducer

B lymphocyte stimulator (BLyS) is a recently identified member of the tumor necrosis factor (TNF) superfamily, which stimulates B lymphocyte’s proliferation and differentiation. The process of expression of hBLyS (human B Lymphocyte cell stimulator) gene under the control of T7 promoter in Escherichia coli was investigated. Lactose was used as an inducer instead of the expensive nonmetabolizable analog of lactose, IPTG. IPTG is satisfactory for small-scale expressions, but not suitable for large-scale fermentations due to its high cost. It was found that lactose could induce foreign protein expression and enhance cell growth during the induction period. Through proper optimization of culture and induction conditions, an expression level near 14.3% of total cellular protein was achieved in the shake flask. This hBLyS expression level reached about 55% of the level (26%) with IPTG as inducer. And in 5 L fermentor, a high cell density OD600=62 and high expression level of hBLyS about16% of the total cell protein were obtained.