Novel Cell Surface Display on Lactic Acid Bacteria and Its Application to Lactic Acid Production from Starchy Materials

Poly lactic acid (PLA) is the one of the important agro-based plastic that can be produced from inexpensive renewable biomass resources including starchy materials. For expanded use of PLA, cost reduction of the lactic acid as a raw material for PLA is very important.

As a novel process for efficient lactic acid production, we propose the use of cell surface display system. This system is based on utilizing naturally occurring cell surface proteins as scaffolds and displaying functional proteins on various cell surfaces. While most of lactic acid bacteria (LAB) can not assimilate starch, by displaying amylase on the cell surfaces of LAB, saccharification of starch and fermentation can be sequentially carried out. Furthermore, since displayed enzymes can be easily separated with the host cells, repeated utilization of enzymes and LAB cells can be achieved. These features will let lactic acid production process to cost-efficient.

In this study, we developed a novel cell surface display system on various kinds of LAB using tandem repeats of the cA peptidoglycan-binding domain that allow efficient display of heterologous proteins. As a result, we succeeded development of the whole cell biocatalyst that possesses high enzyme activity. Finally, using α-amylase displaying LAB, direct and efficient lactic acid fermentation from starch was accomplished.