| Summary: | <i>Tetragenococcus halophilus</i> strains are the halophilic lactic acid bacteria (LAB) that are present in microbial communities during soy sauce or other hyperosmotic foods’ fermentation. This species contributes to the formation of volatiles in fermented foods but may experience harsh conditions such as oxidative stress and osmotic stress during fermentation. The characterization of the oxygen tolerance of <i>T. halophilus</i> and elaboration of its antioxidant mechanism are important for the selection of suitable LAB for food fermentation. In this work, the growth of <i>T. halophilus</i> strains isolated from soy sauce moromi under both aerobic and anaerobic conditions was compared, and the function of their antioxidant enzymes was investigated. These strains showed differences in oxidation resistance, and they all produce antioxidant enzymes including superoxide dismutase, peroxidase and glutathione reductase. Interestingly, genes encoding catalase (CAT) are present in the genome of <i>T. halophilus</i> strains, though some of them are pseudogenes. Catalase produced by <i>T. halophilus</i> belongs to the heme-dependent CAT, and its activity could only be detected in the presence of heme under aerobic condition. The CAT from <i>T. halophilus</i> conditionally contributes to resistance to hydrogen peroxide and oxidative stress. These results elucidated the possible antioxidant mechanism of <i>T. halophilus</i> and revealed the differences in the oxidative stress tolerance of <i>T. halophilus</i> strains.
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