Cloning, expression, and characterization of a Coxiella burnetii Cu/Zn Superoxide dismutase

Background: Periplasmically localized copper-zinc co-factored superoxide dismutase (SodC) enzymes have been identified in a wide range of Gram-negative bacteria and are proposed to protect bacteria from exogenously produced toxic oxygen radicals, which indicates the potential significance of a Coxiella burnetii SodC. Results: Assays for SOD activity demonstrated that the cloned C. burnetii insert codes for a SOD that was active over a wide range of pH and inhibitable with 5 mM H2O2 and 1 mM sodium diethyldithiocarbamate, a characteristic of Cu/ZnSODs that distinguishes them from Fe or Mn SODs. The sodC was expressed by C. burnetii, has a molecular weight of approximately 18 kDa, which is consistent with the predicted molecular weight, and localized towards the periphery of C. burnetii. Over expression of the C. burnetii sodC in an E. coli sodC mutant restored resistance to H2O2 killing to wild type levels. Conclusions: We have demonstrated that C. burnetii does express a Cu/ZnSOD that is functional at low pH, appears to be excreted, and was able to restore H2O2 resistance in an E. coli sodC mutant. Taken together, these results indicate that the C. burnetii Cu/ZnSOD is a potentially important virulence factor.