Cloning and nucleotide sequences of iron and copper-zinc superoxide dismutase genes of Legionella pneumophila and their distribution among Legionella species.

Abstract

A facultative intracellular parasite Legionella pneumophila has two kinds of superoxide dismutase (SOD), iron-containing superoxide dismutase (Fe-SOD) and copper,zinc-containing one (Cu,Zn-SOD). We cloned both SOD genes of L. pneumophila and determined their DNA sequences. The Fe-SOD gene (sodB), isolated by functional complementation of a SOD-deficient Escherichia coli strain, encoded a protein of 192 amino acids conserving the Fe-SOD-specific amino acid residues. A clone containing entire Cu,Zn-SOD gene (sodC) was constructed by connecting two contiguous DNA fragments; one with a lower part of the gene was obtained by colony hybridization with a probe acquired by polymerase chain reaction (PCR) with degenerate oligonucleotide primers corresponding to conserved regions of known Cu,Zn-SOD genes and the other with an upper part of the gene was by IPCR (inverted PCR). The sodC gene encoded a protein of 162 amino acids, of which the first 20 amino acids inferred a signal peptide similar to other bacterial Cu,Zn-SODs reported previously. Both clones expressed their SOD activities in E. coli K-12 through their own plausible promoters. We examined for SOD genes on chromosomes of several Legionella species. All chromosomes were hybridized with Fe-SOD gene of L. pneumophila, but Cu,Zn-SOD gene did not hybridize to the chromosomes of other than L. pneumophila strains.