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[摘要]：Lactic acid bacteria (LAB) are generally sensitive to oxidative stress caused by reactive oxygen species (ROS). Antioxidant enzymes, especially superoxide dismutase (SOD) and catalase (CAT), can protect against ROS by eliminating superoxide and H2O2, respectively. Lactobacillus rhamnosus is a valuable probiotic starter culture but is deficient in both SOD and CAT, and is thus likely to suffer from oxidative stress in industrial fermentation. To confer high level of oxidative resistance on L. rhamnosus, the SOD gene sodA from Streptococcus thermophilus and CAT gene katA from L. sakei were coexpressed in L. rhamnosus AS 1.2466. The enzyme activities of SOD and CAT were 147.80 +/- 1.08 U/mg protein and 2.53 mu mol of H2O2 /min/10(8) cfu, respectively, in the recombinant L. rhamnosus CS. After incubation with 10 mM H2O2, the survival ratio of L, rhamnosus CS was 400-fold higher than that of L. rhamnosus CAT. In long-term aerated conditions, viable cells of L. rhamnosus CS remained similar to 10(6) cfu/mL after incubation for 7 days, while no living cells of the control were detected. These results showed that the cooperation between SOD and CAT could significantly enhance oxidative resistance in L. rhamnosus. To our best knowledge, this is the first report of two synergistic antioxidant genes being coexpressed in the same Lactobacilli. |
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