AUTHOR=Kong Linghui , Xiong Zhiqiang , Song Xin , Xia Yongjun , Zhang Hui , Yang Ying , Ai Lianzhong 

TITLE=Enhanced Antioxidant Activity in Streptococcus thermophilus by High-Level Expression of Superoxide Dismutase

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.579804

DOI=10.3389/fmicb.2020.579804

ISSN=1664-302X

ABSTRACT=<p>Superoxide dismutase (SOD) plays an essential role in eliminating oxidative damage of lactic acid bacteria. <italic>Streptococcus thermophilus</italic>, 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 <italic>sod</italic> gene from <italic>Lactobacillus casei</italic> was heterologous expressed in <italic>S. thermophilus</italic> S-3 using our previous constructed native constitutive promoter library. The enzyme activity of SOD was significantly enhanced in engineered <italic>S. thermophilus</italic> by promoter #14 (2070 U/mg). Furthermore, the strategy of multi-copy <italic>sod</italic>-expressing cassettes was employed to improve SOD activity. The maximum activity (2750 U/mg) was obtained by the two-copy <italic>sod</italic> recombinant, which was 1.5-fold higher than that of one-copy recombinant. In addition, the survival rate of multi-copy <italic>sod</italic> recombinants was increased about 97-fold with 3.5 mmol/L H<sub>2</sub>O<sub>2</sub> treatment. To our knowledge, this is the first report of multi-copy <italic>sod</italic> gene expression in <italic>S. thermophilus</italic>, which exerts a positive effect on coping with oxidative stress to enhance the potential of industrial application.</p>