SALMONELLA-TYPHI MUTANTS DEFECTIVE IN ANAEROBIC RESPIRATION ARE IMPAIRED IN THEIR ABILITY TO REPLICATE WITHIN EPITHELIAL-CELLS

By using MudJ (Kan, lac)-directed operon fusion technology, mutants of Salmonella typhi whose gene expression is induced under anaerobic gro wth 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. An aerobic induction of these fusions did not further increase in respons e to nitrate. Strains carrying an additional mutation in oxrA were con structed. They showed a lower level of beta-galactosidase expression b oth aerobically and anaerobically; however, the ratios of anaerobic in duction 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 (chID)::MudJ insertion a nd the other a moaA (chlA)::MudJ insertion. A third mutant was unable to use either nitrate or fumarate as a terminal electron acceptor. All three mutants showed a reduced ability to enter into and proliferate within HEp-2 epithelial cells. The oxrA mutation enhanced entry and pr oliferation of both the wild-type cells and the three mutants. Taken t ogether, these results suggest that anaerobic respiration plays a role in S. typhi invasiveness.