Expression of tviA is transiently repressed by Hfq in Salmonella enterica serovar Typhi at hyperosmotic stress

The putative global post-transcriptional regulator gene hfq was deleted in Salmonella enterica serovar Typhi (Salmonella typhi). Genomic DNA microarray assay and quantitative real time PCR were used to estimate the level of gene expression. The expression of tviA, the gene required for expression of the Vi capsular antigen, was increased in the hfq mutant at 30 min of an up-shift osmotic stress but was not at sustained high or low osmolarity, compared to the wild type strain. In addition, the level of expression of tviA in the ompR mutant of S. typhi was greatly decreased, similar to what is found in the hfq-ompR double mutant. The results indicate that Hfq negatively regulates the expression of tviA in S. typhi transiently at early stage of hyperosmotic stress.