Proteomic detection of PhoPQ- and acid-mediated repression of Salmonella motility

Abstract

Salmonella adaptation to low pH is a critical survival response and essential for virulence. Here, we show that another key virulence-associated process, flagella-mediated cell motility, is co-regulated by low pH via the PhoPQ signal transduction system. Using a proteomic approach, we found that phase 1 and phase 2 flagellin were specifically down-regulated when acid-adapted (pH 5.0) Salmonella SL1344 cells were exposed to pH 3.0. Decreased flagellin expression and cell motility was dependent on activation of the PhoPQ pathway, which directly or indirectly negatively regulated transcription of the flagellin gene fliC. In contrast, the general stress sigma factor RpoS (sigma s) positively regulated flagellar gene expression. Low external pH had no effect on the level of H-NS protein, a further regulator of flagellar gene expression. We suggest that flagellar repression at low pH conserves ATP for survival processes and helps to limit the influx of protons into the cytosol. These results highlight the power of proteomics to reveal unanticipated links between relatively well-characterised regulatory systems in bacteria.

Flagella-independent surface motility in Salmonella enterica serovar Typhimurium

“…1A), presumably because the PhoP/PhoQ system is not active in high Mg 2+ (11). The identified motility does not appear to be swarming motility because the PhoP/PhoQ system represses flagella-mediated motility (9,10), and one would expect a phoP mutant to move more than the wild-type strain. In addition, swarming motility requires glucose, and the media had glycerol as the carbon source.…”

“…This is because, first, low Mg 2+ activates the PhoP/ PhoQ system, which hinders flagella-mediated motility by repressing transcription of flagellin (9) and by decreasing membrane potential, which hinders flagellar rotation (10). And second, pagM transcription requires the Mg 2+ transporter MgtA and the F 1 F o ATPase inhibitor MgtC.…”

“…For example, the nature of the carbon source is critical because the cAMP-receptor protein promotes transcription of the flagellar master regulator flhDC operon (7), and the RNA binding regulator CsrA furthers stability of the flhDC mRNA (8). By contrast, the PhoP/PhoQ regulatory system down-regulates flagella-mediated motility by repressing transcription of flagellar genes (9) and by decreasing the membrane potential (10).…”

Adaptation of Salmonella to Antimicrobials in Food-Processing Environments

“…Similarly, the long-term adaptation of Salmonella to propionate reduced the overall infectivity of the adapted cells by inhibiting the colonization ability of the organism . Moreover, flagella motility, which is fundamental to the virulence process, was shown to be repressed at a low pH in order to allow the conservation of ATP for survival processes (Adams et al, 2001). …”

Post-genomics ofNeisseria meningitidis: an update

“…[34] and its functional homologs, such as the meningococcal NMB0595/ NMB0594 system [31][32][33]. As a consequence, microarray transcription profile comparison has been frequently used to explore the meningococcal NMB0595/NMB0594 two-component regulatory system activity at the physiological level [35].…”