Protective role of glutathione against oxidative stress in Streptococcus thermophilus

Streptococcus thermophilus can grow in the presence of oxygen and survive at low concentrations of H2O2. Glutathione (GSH) plays an important role in living cells, but its protective roles against oxidative stress in S. thermophilus remain unclear. We assessed intracellular GSH accumulation under both anaerobic and aerobic growth conditions in 40 S. thermophilus strains. The GSH level in different strains was found to be strain-specific. A gshF gene, encoding the GSH synthesis, was inactivated in the genome of strain SDMCC18. The growth and survival of the resulting mutant SDMCC18ΔgshF were significantly reduced after exposure to oxygen and H2O2. However, the oxidative tolerance of the mutant strain was restored by exogenous GSH. Our findings provide a new strategy to improve the robustness of S. thermophilus in starter manufacture and industrial applications. We, for the first time, demonstrated the GSH synthesis and its transport from the culture medium in S. thermophilus.