The Bacterial Cytoskeleton Modulates Motility, Type 3 Secretion, and Colonization in Salmonella

Abstract

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 ΔmreC 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 ΔmreC 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 ΔmreC. 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.

RcsB positively regulates the Yersinia Ysc‐Yop type III secretion system by activating expression of the master transcriptional regulator LcrF

“…Interestingly, previous studies have indicated that the Rcs system regulates the expression of the genome encoded Ysa‐T3SS in Y. enterocolitica (Venecia and Young, ; Walker and Miller, ), as well as T3SS in Salmonella enterica serotype Typhi ( S. Typhi) (Arricau et al ., ; Lin et al ., ; Bulmer et al ., ). In the present study, we identified and characterized a regulatory role of Rcs system in controlling Yersinia Ysc‐Yop T3SS.…”

Genomic variations leading to alterations in cell morphology of Campylobacter spp

“…maintain their cell shape and thus any associated colonisation, pathogenic or other advantage, it is first important to identify the genes and proteins involved. While the C. jejuni genome encodes cytoskeleton regulatory elements MreB, RodA and FtsZ, important for maintaining rod morphology in many bacteria111213141516, these proteins alone are not sufficient to generate helical and curved bacterial morphologies111718. Mechanisms for generating helical and curved morphologies have been identified in other bacterial species, including the proteins encoded by the genes ccrp59, ccrp1143, csd1, csd2, csd3 and ccmA in Helicobacter pylori 1920 and creS in Caulobacter crescentus 21.…”

5′-UTR of malS Increases the Invasive Capacity of Salmonella Enterica Serovar Typhi by Influencing the Expression of Bax

“…The transcription of flagellar genes is organized into a regulatory hierarchy of class I, II and III genes [31]. FliA alone or with FlhDC activates the expression of the class III genes, which encode the filament protein and motor proteins [32]. FliC is the major component of the flagellum and the deletion of fliC reduces bacterial motility.…”