Salmonella enterica serovar Typhi z66-positive strains have two different flagellin genes, fliC:d/j and
fljB:z66, located on the chromosome and on a linear plasmid, respectively. To investigate the mechanism
underlying the expressional regulation of fljB:z66, gene deletion mutants of the regulators FliA, FlhDC,
and OmpR were constructed in this study. The expression levels of fliC and fljB:z66 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 fljB:z66 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 fljB:z66, fliC, fliA, and
flhD were increased at low osmotic conditions. SDS-PAGE and western blotting analysis of the secreted
proteins revealed that the FljB:z66 was almost absent in the fliA and flhDC mutants at both high and low
osmolarity. In the wild-type strain, the fljB:z66 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 FljB:z66 showed that the FljB:z66 expression was
decreased in ompR mutant at both low and high osmolarity. These results suggest that the expression of
fljB:z66 in S. enterica serovar Typhi is dependent on FliA and FlihDC, and OmpR can regulate the
expression and secretion of FljB:z66 in different osmolarity.
