Interaction between Bifidobacterium bifidum and Listeria monocytogenes enhances antioxidant activity through oxidoreductase system

In this study, we found that the antioxidant activity of Bifidobacterium bifidum WBBI03 and Listeria monocytogenes CMCC 54001 was increased after co-incubation. Therefore, the molecular mechanism of enhancing antioxidant activity was explored through isobaric tags for relative and absolute quantitation (iTRAQ). Analysis of differentially expressed proteins revealed increased expression of a series of antioxidant-related proteins, including glutaredoxin and thioredoxin in B. bifidum WBBI03, and universal stress protein UspA and aldo/keto reductase in L. monocytogenes CMCC 54001. Based on previous studies, certain antioxidant genes were selected for fluorescence quantitative PCR analysis to find out transcriptionally up-regulated genes. It was also detected that superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX) enzyme activities increased after interaction of the two strains. These results may partially explain the improved survival of B. bifidum WBBI03 and L. monocytogenes CMCC 54001 after interaction in strong oxidizing environments containing hydrogen peroxide or cumene hydroperoxide (CHP). It is speculated that L. monocytogenes (a representative opportunistic pathogenic bacterium) may help B. bifidum (a representative probiotic bacterium) to resist damages caused by oxygen species in the gastrointestinal tract, which may part of the biological significance of its presence in the intestinal microbial ecosystem.