Salmonella enterica serovar Typhimurium NiFe uptake-type hydrogenases are differentially expressed in vivo

Salmonella enterica serovar Typhimurium, a common enteric pathogen, possesses three NiFe uptake-type hydrogenases. The results from mouse infection studies suggest that the H(2) oxidation capacity provided by these hydrogenases is important for virulence. Since the three enzymes are similar in structure and function, it may be expected that they are utilized under different locations and times during an infection. A recombination-based method to examine promoter activity in vivo (RIVET) was used to determine hydrogenase gene expression in macrophages, polymorphonuclear leukocyte (PMN)-like cells, and a mouse model of salmonellosis. The hyd and hya promoters showed increased expression in both murine macrophages and human PMN-like cells compared to that in the medium-only controls. Quantitative reverse transcription-PCR results suggested that hyb is also expressed in phagocytes. A nonpolar hya mutant was compromised for survival in macrophages compared to the wild type. This may be due to lower tolerance to acid stress, since the hya mutant was much more acid sensitive than the wild type. In addition, hya mutant cells were internalized by macrophages the same as wild-type cells. Mouse studies (RIVET) indicate that hyd is highly expressed in the liver and spleen early during infection but is expressed poorly in the ileum in infected animals. Late in the infection, the hyd genes were expressed at high levels in the ileum as well as in the liver and spleen. The hya genes were expressed at low levels in all locations tested. These results suggest that the hydrogenases are used to oxidize hydrogen in different stages of an infection.