GENETIC, ENZYMATIC, AND PATHOGENIC STUDIES OF THE IRON SUPEROXIDE-DISMUTASE OF CAMPYLOBACTER-JEJUNI

Campylobacter jejuni is a microaerobic bacterium that produces an acut e, self-limiting, watery or bloody diarrhea in humans. Little is known about how C. jejuni causes disease or even what specific capabilities it requires for survival in vivo. The enzyme, superoxide dismutase (S OD), which catalyzes the breakdown of superoxide radicals to hydrogen peroxide and dioxygen is one of the bacterial cell's major defense mec hanisms against oxidative damage. A PCR-based search for sod genes in C. jejuni 81-176 revealed that this bacterium contained at least one s od gene. We cloned and sequenced a sod gene from 81-176 and determined that its predicted protein product was most similar to that of FeSODs (sodB genes). Transcriptional analysis indicated that this gene is mo nocistronic and may be transcribed from a sigma(70)-like promoter. Non denaturing polyacrylamide gels stained to reveal SOD activities, accom panied by inhibition studies, demonstrated that C. jejuni produces fiv e electrophoretically distinct bands of SOD activity, all of which app eared to be FeSODs. Analysis of an 81-176 sodB strain revealed that al l of these FeSOD activities may be products of the one sodB gene that we cloned. The expression and enzymatic activity of the respective sod B and FeSOD produced by both C. jejuni and Helicobacter pylori were ex amined in Escherichia coli. Both genes were expressed in E. coli, and the proteins produced were enzymatically active. Finally, the ability of the 81-176 sodB strain to survive INT407 cell invasion was found to be significantly decreased (12-fold) compared with that of the parent , suggesting a potential role for SodB in C.jejuni intracellular survi val.