Although there have been great advances in our understanding of the bacterial cytoskeleton, major gaps remain in our
knowledge of its importance to virulence. In this study we have explored the contribution of the bacterial cytoskeleton to
the ability of Salmonella to express and assemble virulence factors and cause disease. The bacterial actin-like protein MreB
polymerises into helical filaments and interacts with other cytoskeletal elements including MreC to control cell-shape. As
mreB appears to be an essential gene, we have constructed a viable DmreC depletion mutant in Salmonella. Using a broad
range of independent biochemical, fluorescence and phenotypic screens we provide evidence that the Salmonella
pathogenicity island-1 type three secretion system (SPI1-T3SS) and flagella systems are down-regulated in the absence of
MreC. In contrast the SPI-2 T3SS appears to remain functional. The phenotypes have been further validated using a chemical
genetic approach to disrupt the functionality of MreB. Although the fitness of DmreC is reduced in vivo, we observed that
this defect does not completely abrogate the ability of Salmonella to cause disease systemically. By forcing on expression of
flagella and SPI-1 T3SS in trans with the master regulators FlhDC and HilA, it is clear that the cytoskeleton is dispensable for
the assembly of these structures but essential for their expression. As two-component systems are involved in sensing and
adapting to environmental and cell surface signals, we have constructed and screened a panel of such mutants and
identified the sensor kinase RcsC as a key phenotypic regulator in DmreC. Further genetic analysis revealed the importance
of the Rcs two-component system in modulating the expression of these virulence factors. Collectively, these results
suggest that expression of virulence genes might be directly coordinated with cytoskeletal integrity, and this regulation is
mediated by the two-component system sensor kinase RcsC.