Optimization of medium components
TBSB was used as the initial medium for medium components optimization. For carbon source optimization, 10 g/L glucose, fructose, xylose, and sucrose were added into the TBSB medium to replace the original glycerin. The cell growth and protein production using glucose carbon source were used as control. For nitrogen source optimization, additional 10 g/L urea, (NH4)2SO4, and NH4Cl was added to the TBSB medium, and the protein yield and OD600 in the TBSB medium were used as control. For all medium optimization experiments, the cultivation and induction condition was set at the optimal level previously determined.