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Infect. Immun. doi:10.1128/IAI.01556-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Characterization of SodC, a Periplasmic Superoxide Dismutase from Burkholderia cenocepacia

Infectious Diseases Research Group, Siebens-Drake Research Institute, Departments of Microbiology and Immunology, and Medicine, University of Western Ontario, London, Ontario, N6A 5C1, Canada

^* To whom correspondence should be addressed. Email: mvalvano{at}uwo.ca.

	Abstract

Burkholderia cenocepacia is a gram-negative, non-spore forming bacillus and a member of the B. cepacia complex (Bcc). B. cenocepacia can survive intracellularly in phagocytic cells and can produce at least one superoxide dismutase (SOD). The inability of O₂^- to cross the cytoplasmic membrane, coupled with the periplasmic location of Cu,ZnSODs, suggests that periplasmic SODs protect bacteria from superoxide of exogenous origin, for example when faced with reactive oxygen intermediates generated by host cells in response to infection. In this study, we have identified the sodC gene, encoding a Cu,ZnSOD in B. cenocepacia, and demonstrate that a sodC null mutant was not sensitive to H₂O₂, SIN-1 or paraquat challenge but was killed by exogenous superoxide generated by the xanthine/xanthine oxidase method. The sodC mutant also displayed a growth defect in liquid medium compared to the parental strain, which could be complemented in trans. The mutant was killed more rapidly than the parental strain in the murine macrophage-like cell line RAW 264.7, but killing was abrogated in macrophages treated with an NADPH oxidase inhibitor. We also confirmed that SodC is periplasmic and identified the metal-cofactor. B. cenocepacia SodC was resistant to inhibition by H₂O₂ and unusually resistant to KCN for a Cu,ZnSOD. Together, these observations establish that B. cenocepacia produces a periplasmic Cu,ZnSOD that protects the bacterium from exogenously generated O₂^- and contributes to bacterial intracellular survival in macrophages.

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