superoxide reductase mitigates oxygen sensitivity.

causes a serious diarrheal disease and is a common healthcare-associated bacterial pathogen. Although it has a major impact on human health, the mechanistic details of intestinal colonization remain undefined. is highly sensitive to oxygen and requires anaerobic conditions for growth. However, the mammalian gut is not devoid of oxygen, and tolerates moderate oxidative stress . The genome encodes several antioxidant proteins, including a predicted superoxide reductase (SOR) that is upregulated upon exposure to antimicrobial peptides. The goal of this study was to establish SOR enzymatic activity and assess its role in protecting against oxygen exposure. Insertional inactivation of rendered more sensitive to superoxide, indicating that SOR contributes to antioxidant defense. Heterologous expression in conferred protection against superoxide-dependent growth inhibition, and the corresponding cell lysates showed superoxide scavenging activity. Finally, a SOR mutant exhibited global proteome changes under oxygen stress when compared to the parent strain. Collectively, our data establish the enzymatic activity of SOR, confirm its role in protection against oxidative stress, and demonstrate SOR's broader impacts on the vegetative cell proteome.IMPORTANCE is an important pathogen strongly associated with healthcare settings and capable of causing severe diarrheal disease. While considered a strict anaerobe , has been shown to tolerate low levels of oxygen in the mammalian host. Among other well-characterized antioxidant proteins, the genome encodes a predicted superoxide reductase (SOR), an understudied component of antioxidant defense in pathogens. The significance of the research reported herein is the characterization of SOR's enzymatic activity, including confirmation of its role in protecting against oxidative stress. This furthers our understanding of pathogenesis and presents a potential new avenue for targeted therapies.