Regulation of EPS production in Lactobacillus casei LC2W through metabolic engineering.

Lactobacillus casei LC2W is an exopolysaccharide(EPS)-producing strain with probiotic effects. The low efficiency and unclear regulation mechanism of EPS biosynthesis have become main constraints for its application in food industry. To investigate the major rate-limiting factors of EPS biosynthesis and to improve its yield, metabolic engineering was applied to this strain. Eight relevant genes related to central metabolism, sugar-nucleotides supply, glycosyltransferase and cofactor engineering were cloned and overexpressed. The results suggested that nox, pfk, rfbB and galT genes were the largest contributors to EPS biosynthesis in this study, which elevated EPS yield by 46·0, 20, 17·4 and 19·6% respectively. Notably, under aerobic condition which was not a suitable condition for lactobacilli to grow in, recombinant strain LC-nox achieved the highest EPS yield of 263·7 mg l–1, which was increased by 75% compared to that of the starting strain. The oxygen stress was excluded since the phenomenon was not observed in the control strain under the same condition. Therefore, it was probably that higher NADH oxidase activity led to a decreased NADH availability and reduced lactate concentration, which resulted in the elevation of EPS yield. [ABSTRACT FROM AUTHOR]