Impact of overexpression of NADH oxidase on exopolysaccharide production in Lactobacillus casei LC2W

To investigate the effect of NADH oxidase gene(nox) on the production of exopolysaccharide from Lactobacillus casei LC2 W,nox gene was obtained by PCR amplification with the genomic DNA of Streptococcus mutans as template. It was subcloned into a lactobacilli vector to construct the recombinant expression plasmid p IB184-nox. By electroporation,p IB184-nox was introduced into Lactobacillus casei LC2 W,resulting in the recombinant strain designated as LC-nox. Under anaerobic condition,LC-nox overexpressed NADH oxidase to a level of 0.7 U/m L,while it was elevated to 2.65 U/m L under aerobic condition. Detected by HPLC,the lactate concentration in the fermentation broth showed negative correlation with NADH oxidase activity. The carbon source saved was used for the biosynthesis of exopolysaccharide(EPS). The highest yield of EPS was reached at 263.7 mg/L under aerobic fermentation,which was increased by 75.4% compared to that of the starting strain. A novel theoretical basis was provided for the regulation of EPS biosynthesis in lactobacillus.