Salmonella typhi mutants defective in anaerobic respiration are impaired in their ability to replicate within epithelial cells

Abstract

By using MudJ (Kan, lac)-directed operon fusion technology, mutants of Salmonella typhi whose gene expression is induced under anaerobic growth conditions were isolated. Characterization of their phenotypes and regulatory properties revealed that two of the mutants were unable to use nitrate as a terminal electron acceptor in the absence of oxygen, suggesting that they were defective in nitrate reductase activity. Anaerobic induction of these fusions did not further increase in response to nitrate. Strains carrying an additional mutation in oxrA were constructed.They showed a lower level of β-galactosidase expression both aerobically and anaerobically; however, the ratios of anaerobic induction remained unaltered. These MudJ insertions mapped to the 17-19 min region of the chromosome. Based upon their phenotypes and mapping, one of the mutants probably possessed a modC (chlD)::MudJ insertion and the other a moaA (chlA)::MudJ insertion. A third mutant was unable to use either nitrate or