The iron superoxide dismutase of Legionella pneumophila is essential for viability.
Legionella pneumophila, the causative agent of Legionnaires' disease, contains two superoxide dismutases (SODs), a cytoplasmic iron enzyme (FeSOD) and a periplasmic copper-zinc SOD. To study the role of the FeSOD in L. pneumophila, the cloned FeSOD gene (sodB) was inactivated with Tn903dIIlacZ, forming a sodB::lacZ gene fusion. By using this fusion, expression of sodB was shown to be unaffected by a variety of conditions, including several that influence sod expression in Escherichia coli: aeration, oxidants, the redox cycling compound paraquat, manipulation of iron levels in the medium, and the stage of growth. A reproducible twofold decrease in sodB expression was found during growth on agar medium containing charcoal, a potential scavenger of oxyradicals, in comparison with growth on the same medium without charcoal. No induction was seen during growth in human macrophages. Additional copies of sodB+ in trans increased resistance to paraquat. Construction of a sodB mutant was attempted by allelic exchange of the sodB::lacZ fusion with the chromosomal copy of sodB. The mutant could not be isolated, and the allelic exchange was possible only if wild-type sodB was present in trans. These results indicate that the periplasmic copper-zinc SOD cannot replace the FeSOD. The data strongly suggest that sodB is an essential gene and that FeSOD is required for the viability of L. pneumophila. In contrast, Sod- mutants of E. coli and Streptococcus mutans grow aerobically and SOD is not required for viability in these species.
Sadosky
A B
AB
Department of Microbiology, College of Physicians and Surgeons of Columbia University, New York, New York 10032.
Wilson
J W
JW
Steinman
H M
HM
Shuman
H A
HA
D000154:Aconitate Hydratase / Q000032:analysis; D000483:Alleles; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D003001:Cloning, Molecular; D004171:Diploidy; D004352:Drug Resistance, Microbial; D005798:Genes, Bacterial / Q000235:genetics*; D005804:Genes, Lethal / Q000235:genetics*; D007763:Lac Operon / Q000235:genetics; D016952:Legionella pneumophila / Q000201:enzymology / Q000235:genetics / Q000254:growth & development*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D016366:Open Reading Frames / Q000235:genetics; D010269:Paraquat / Q000494:pharmacology; D011993:Recombinant Fusion Proteins / Q000235:genetics; D017422:Sequence Analysis, DNA; D013482:Superoxide Dismutase / Q000235:genetics*
D001426:Bacterial Proteins; D011993:Recombinant Fusion Proteins; C087504:SodB protein, Bacteria; D013482:Superoxide Dismutase; D000154:Aconitate Hydratase; D010269:Paraquat