Approaches for improving protein production by cell surface engineering

Bacillus subtilis is an attractive host organism because it has a naturally high secretory capacity and exports proteins directly into the extracellular medium. Secreted proteins emerge from translocation to the compartment between the cell wall and cytoplasmic membrane. It has been reported that the increased net negative charge of the cell wall is involved in protein folding and stability at the cytoplasmic membrane-cell wall interface of B. subtilis. In Escherichia coli, Sec translocase requires a functional interaction with the membrane acidic lipids such as phosphatidylglycerol (PG) and cardiolipin (CL). In Sect. 13.1, we describe altered compositions of anionic polymers on the cell surface and cell membrane lipid of B. subtilis, which is improved for protein secretion. Inactivation of extracellular proteases is essential for improvement of secreted proteins with B. subtilis as a host. Previously we reported that the decrease of extracellular protease amounts in B. subtilis mutants led to the stabilization of autolysins, making the cells more prone to lysis (Kodama et al., J Biosci Bioeng 103:13-21, 2007). In Sect. 13.2, we describe the improvement process for protein production from the aspect of prevention of cell lysis.