title: Identification of Francisella tularensis live vaccine strain CuZn superoxide dismutase as critical for resistance to extracellularly generated reactive oxygen species.
abstract: Francisella tularensis is an intracellular pathogen whose survival is in part dependent on its ability to resist the microbicidal activity of host-generated reactive oxygen species (ROS) and reactive nitrogen species (RNS). In numerous bacterial pathogens, CuZn-containing superoxide dismutases (SodC) are important virulence factors, localizing to the periplasm to offer protection from host-derived superoxide radicals (O(2)(-)). In the present study, mutants of F. tularensis live vaccine strain (LVS) deficient in superoxide dismutases (SODs) were used to examine their role in defense against ROS/RNS-mediated microbicidal activity of infected macrophages. An in-frame deletion F. tularensis mutant of sodC (DeltasodC) and a F. tularensis DeltasodC mutant with attenuated Fe-superoxide dismutase (sodB) gene expression (sodB DeltasodC) were constructed and evaluated for susceptibility to ROS and RNS in gamma interferon (IFN-gamma)-activated macrophages and a mouse model of respiratory tularemia. The F. tularensis DeltasodC and sodB DeltasodC mutants showed attenuated intramacrophage survival in IFN-gamma-activated macrophages compared to the wild-type F. tularensis LVS. Transcomplementing the sodC gene in the DeltasodC mutant or inhibiting the IFN-gamma-dependent production of O(2)(-) or nitric oxide (NO) enhanced intramacrophage survival of the sod mutants. The DeltasodC and sodB DeltasodC mutants were also significantly attenuated for virulence in intranasally challenged C57BL/6 mice compared to the wild-type F. tularensis LVS. As observed for macrophages, the virulence of the DeltasodC mutant was restored in ifn-gamma(-/-), inos(-/-), and phox(-/-) mice, indicating that SodC is required for resisting host-generated ROS. To conclude, this study demonstrates that SodB and SodC act to confer protection against host-derived oxidants and contribute to intramacrophage survival and virulence of F. tularensis in mice.
authors.affiliation: Center for Immunology and Microbial Disease, MC 151, Albany Medical College, 47 New Scotland Ave., Albany, NY 12208, USA.
authors.forename: Amanda A
authors.initials: AA
authors.lastname: Melillo
authors.forename: Manish
authors.initials: M
authors.lastname: Mahawar
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Sellati
authors.forename: Meenakshi
authors.initials: M
authors.lastname: Malik
authors.forename: Dennis W
authors.initials: DW
authors.lastname: Metzger
authors.forename: J Andres
authors.initials: JA
authors.lastname: Melendez
authors.forename: Chandra Shekhar
authors.initials: CS
authors.lastname: Bakshi
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001428:Bacterial Vaccines; D005604:Francisella tularensis / Q000145:classification / Q000187:drug effects / Q000201:enzymology* / Q000472:pathogenicity; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D016676:Macrophages, Alveolar / Q000382:microbiology; D051379:Mice; D009154:Mutation; D026361:Reactive Nitrogen Species; D017382:Reactive Oxygen Species / Q000494:pharmacology*; D013482:Superoxide Dismutase / Q000378:metabolism*; D014406:Tularemia / Q000382:microbiology; D014774:Virulence
chemical_list: D001426:Bacterial Proteins; D001428:Bacterial Vaccines; D026361:Reactive Nitrogen Species; D017382:Reactive Oxygen Species; D013482:Superoxide Dismutase
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