Salmonella Biofilm Development Depends on the Phosphorylation Status of RcsB

Abstract

The Rcs phosphorelay pathway is a complex signaling pathway involved in the regulation of many cell surface structures in enteric bacteria. In response to environmental stimuli, the sensor histidine kinase (RcsC) autophosphorylates and then transfers the phosphate through intermediary steps to the response regulator (RcsB), which, once phosphorylated, regulates gene expression. Here, we show that Salmonella biofilm development depends on the phosphorylation status of RcsB. Thus, unphosphorylated RcsB, hitherto assumed to be inactive, is essential to activate the expression of the biofilm matrix compounds. The prevention of RcsB phosphorylation either by the disruption of the phosphorelay at the RcsC or RcsD level or by the production of a nonphosphorylatable RcsB allele induces biofilm development. On the contrary, the phosphorylation of RcsB by the constitutive activation of the Rcs pathway inhibits biofilm development, an effect that can be counteracted by the introduction of a nonphosphorylatable RcsB allele. The inhibition of biofilm development by phosphorylated RcsB is due to the repression of CsgD expression, through a mechanism dependent on the accumulation of the small noncoding RNA RprA. Our results indicate that unphosphorylated RcsB plays an active role for integrating environmental signals and, more broadly, that RcsB phosphorylation acts as a key switch between planktonic and sessile life-styles in Salmonella enterica serovar Typhimurium.

Small RNA-based feedforward loop with AND-gate logic regulates extrachromosomal DNA transfer in Salmonella

“…1C). We did not observe the previously reported RprA-mediated repression of csgD (35,36), perhaps because the csgD promoter was silent under the experimental conditions used here (37). This notwithstanding, our pulse expression data suggested that the two forms of RprA recognize several targets by different seed regions and predicted processed RprA to be a regulator in its own right.…”

Dam methylation is required for efficient biofilm production in Salmonella enterica serovar Enteritidis

“…S1, supplementary file). A decreased expression of csgA as a result of a diminished expression of csgD, has been reported earlier in S. Typhimurium (Baugh et al, 2012;Latasa et al, 2012). Additionally, the expression of csgA was significantly increased in the clinical isolate compared with the reference wild type strain.…”

“…Briefly, 1 colony-forming unit of Salmonella was grown in 5 ml of LBNaCl−, pH 7.0, at 28°C and 200 rpm for 12 h, in 15 ml glass tubes. Agitation was stopped and static cultures were tested visually and photographed by a digital camera every 24 h for 72 h. Biofilm development was visualized as a floating pellicle at the air -broth interface (Latasa et al, 2012). The following scoring scheme was first described by Cisar et al (1979) and adapted for this work: 0, no pellicle formation; 1, very small and non-uniform pellicle; 2, easily visible pellicle that can be dispersed by shaking; 3, clearly visible pellicle non-dense which cannot be dispersed by shaking; and 4, dense pellicle which totally blocks the surface of the culture and cannot be dispersed by shaking.…”

Unexpected properties of sRNA promoters allow feedback control via regulation of a two-component system

“…In some cases, the unphosphorylated form of a response regulator has been shown to specifically activate gene expression at some target-promoters (e.g. 58,59). However, in the case studied here, our results suggest that at least some OmpR-P is required for transcription activation at the Omr promoters.…”