Identification and Characterization of a Second Superoxide Dismutase Gene ( sodM ) from Staphylococcus aureus

Abstract

A gene encoding superoxide dismutase (SOD), sodM, from S. aureus was cloned and characterized. The deduced amino acid sequence specifies a 187-amino-acid protein with 75% identity to the S. aureus SodA protein. Amino acid sequence comparisons with known SODs and relative insensitivity to hydrogen peroxide and potassium cyanide indicate that SodM most likely uses manganese (Mn) as a cofactor. The sodM gene expressed from a plasmid rescued an Escherichia coli double mutant (sodA sodB) under conditions that are otherwise lethal. SOD activity gels of S. aureus RN6390 whole-cell lysates revealed three closely migrating bands of activity. The two upper bands were absent in a sodM mutant, while the two lower bands were absent in a sodA mutant. Thus, the middle band of activity most likely represents a SodM-SodA hybrid protein. All three bands of activity increased as highly aerated cultures entered the late exponential phase of growth, SodM more so than SodA. Viability of the sodA and sodM sodA mutants but not the sodM mutant was drastically reduced under oxidative stress conditions generated by methyl viologen (MV) added during the early exponential phase of growth. However, only the viability of the sodM sodA mutant was reduced when MV was added during the late exponential and stationary phases of growth. These data indicate that while SodA may be the major SOD activity in S. aureus throughout all stages of growth, SodM, under oxidative stress, becomes a major source of activity during the late exponential and stationary phases of growth such that viability and growth of an S. aureus sodA mutant are maintained.Staphylococcus aureus is a gram-positive facultative anaerobe that typically resides on the skin and mucous membranes of approximately 30% of healthy individuals and up to 90% of health care workers (42). Therefore, it is not surprising that of the estimated 2 million hospitalizations each year that result in a nosocomial infection, S. aureus is one of the most common causative agents (5, 15). S. aureus has the capacity to produce more than 30 secreted proteins in the form of enzymes, immunotoxins, and cytotoxins and numerous cell surface-associated factors that promote adherence to various tissues and prevent attack by the host's defenses (17, 36). Consequently, S. aureus causes numerous different kinds of infections, ranging from skin abscesses to life-threatening endocarditis, meningitis, and pneumonia as well as toxemias such as scalded skin and toxic shock syndromes (42).The skin and mucous membranes serve as the primary line of defense against infection by S. aureus (41). However, when this organism is introduced into the underlying tissues, the primary defense mechanism is the professional phagocyte (41). Polymorphonuclear leukocytes and macrophages use toxic reactive oxygen intermediates such as superoxide and hydrogen peroxide to aid in the killing of phagocytized bacteria (11,22,35). In addition, these same oxygen species are produced during aerobic respiration and have the potential to damage DNA, p...

Molecular basis for manganese sequestration by calprotectin and roles in the innate immune response to invading bacterial pathogens

“…Although little is known about the role of Mn in bacterial physiology and pathogenesis, it plays critical roles in metabolism, the response to oxidative stress, and other bacterial processes (22)(23)(24). Understanding of bacterial physiology is advancing at a rapid pace, and we expect that additional Mndependent pathways will soon be discovered.…”

“…Specifically, CP inactivates staphylococcal superoxide dismutases (SOD) and increases the sensitivity of S. aureus to exogenous oxidative stress (13). Given the Mn dependency of the only two SODs expressed by S. aureus, SodA and SodM, it is likely that inhibition of these processes by CP is due to Mn sequestration (23,24). To test this hypothesis, the ability of ΔS1 and ΔS2 CP to increase S. aureus sensitivity to superoxide, elevate intracellular superoxide levels, and reduce SOD activity was assessed.…”

“…To test this hypothesis, the ability of ΔS1 and ΔS2 CP to increase S. aureus sensitivity to superoxide, elevate intracellular superoxide levels, and reduce SOD activity was assessed. As an initial test, S. aureus was treated with WT CP, ΔS1, or ΔS2 and assessed for sensitivity to the superoxide-generating compound paraquat whose toxicity is greatly increased in SOD-deficient strains (13,24,25). WT CP and the ΔS2 mutant increased the sensitivity of S. aureus to paraquat whereas ΔS1 did not (Fig.…”

Oxidative-stress-inducible qorA encodes an NADPH-dependent quinone oxidoreductase catalysing a one-electron reduction in Staphylococcus aureus

“…To confront these ROS, S. aureus produces antioxidant enzymes including superoxide dismutase (SOD) Valderas & Hart, 2001) and catalase (Sanz et al, 2000). SOD is a major important enzyme in scavenging superoxide anions, which are reduced to hydrogen peroxide.…”

16S rDNA-Based Identification of Novel Superoxide Dismutase Producing Bacteria Isolated from Indonesia

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