Enhanced Antioxidant Activity in by High-Level Expression of Superoxide Dismutase.

Superoxide dismutase (SOD) plays an essential role in eliminating oxidative damage of lactic acid bacteria. , an important probiotic lactic acid bacterium, often inevitably suffers from various oxidative stress during dairy fermentation. In this study, to confer high-level oxidative resistance, the gene from was heterologous expressed in S-3 using our previous constructed native constitutive promoter library. The enzyme activity of SOD was significantly enhanced in engineered by promoter #14 (2070 U/mg). Furthermore, the strategy of multi-copy -expressing cassettes was employed to improve SOD activity. The maximum activity (2750 U/mg) was obtained by the two-copy recombinant, which was 1.5-fold higher than that of one-copy recombinant. In addition, the survival rate of multi-copy recombinants was increased about 97-fold with 3.5 mmol/L HO treatment. To our knowledge, this is the first report of multi-copy gene expression in , which exerts a positive effect on coping with oxidative stress to enhance the potential of industrial application.