Expression of fljB: z66 on a linear plasmid of Salmonella enterica serovar typhi is dependent on FliA and FlhDC and regulated by OmpR

ABSTRACT

Salmonella enterica serovar Typhi z66-positive strains have two different flagellin genes, fliCd/j and fljBz66, located on the chromosome and on a linear plasmid, respectively. To investigate the mechanism underlying the expressional regulation of fljBz66, gene deletion mutants of the regulators FliA, FlhDC, and OmpR were constructed in this study. The expression levels of fliC and fljBz66 were analyzed by qRT-PCR in the wild-type strain and mutants at high and low osmolarity. The results show that the expression levels of both fljBz66 and fliC were greatly reduced in fliA and flhDC mutants under both high and low osmotic conditions. In the ompR mutant, the expression levels of fljBz66, fliC, fliA, and flhD were increased at low osmotic conditions. SDS-PAGE and western blotting analysis of the secreted proteins revealed that the FljBz66 was almost absent in the fliA and flhDC mutants at both high and low osmolarity. In the wild-type strain, the fljBz66 was more highly expressed under high-osmolarity conditions than under low-osmolarity conditions. However, this difference in expression disappeared in the ompR mutant. Translational expression assay of FljBz66 showed that the FljBz66 expression was decreased in ompR mutant at both low and high osmolarity. These results suggest that the expression of fljBz66 in S. enterica serovar Typhi is dependent on FliA and FlihDC, and OmpR can regulate the expression and secretion of FljBz66 in different osmolarity.