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李 寅江南大学工业生物技术教育部重点实验室 In this study we aim to characterize GSH accumulation and its role in lactic acid bacteria. Defined starter cultures of L. lactis are of great economic importance in the bulk production of Cheese. As a facultative anaerobe, strains of L. lactis very often encounter a challenge from oxygen and they have evolved several systems, e.g. NADH oxidase/NADH perosidase system, to survive this challenge (6). The glutathione-dependent reduction system is responsible for maintaining the reduced environment and plays an important role against oxidative stress in E. coli and S. cerevisiae (4). However, the physiological role of GSH in L. lactis, or even in gram-positive bacteria, remains unknown except that Sherrill and Fahey (22) found the cellular glutathione of Streptococcus mutans ATCC 33402 protected cells against growth inhibition caused by a specific thiol oxidizing agent diamide. We therefore examined the presence of GSH and glutathione-dependent enzymes, e.g. glutathione reductase (GR), in different strains of L. lactis. All the subspecies of dairy L. lactis were unable to synthesize GSH but some strains could import it from the medium. In addition, glutathione reductase was observed to be a ubiquitous enzyme in L. lactis, and the activity of this enzyme was sensitive to oxygenation. Using L. lactis SK11 as a model strain, we demonstrated that stationary phase cells with intracellular GSH had a strong resistance against H2O2 treatment compared to cells without intracellular GSH, which exhibited as a high survival and a shortened lag phase as well. Furthermore, the lag phase difference upon H2O2 treatment was found to be dependent on the ability to take up glutathione in the 16 tested strains of L. lactis. To our best knowledge, this is the first report with respect to a clear physiological role of glutathione in lactic acid bacteria. In addition, our insights on the presence and protection role of GSH in L. lactis could be applied to dairy indu