The Rcs phosphorelay system is specific to enteric pathogens/commensals and activates ydeI, a gene important for persistent Salmonella infection of mice

Abstract

SummaryBacteria utilize phosphorelay systems to respond to environmental or intracellular stimuli. Salmonella enterica encodes a four-step phosphorelay system that involves two sensor kinase proteins, RcsC and RcsD, and a response regulator, RcsB. The physiological stimulus for Rcs phosphorelay activation is unknown; however, Rcs-regulated genes can be induced in vitro by osmotic shock, low temperature and antimicrobial peptide exposure. In this report we investigate the role of the Rcs pathway using phylogenetic analysis and experimental techniques. Phylogenetic analysis determined that full-length RcsCand RcsD-like proteins are generally restricted to Enterobacteriaceae species that have an enteric pathogenic or commensal relationship with the host. Experimental data show that RcsD and RcsB, in addition to RcsC, are important for systemic infection in mice and polymyxin B resistance in vitro. To identify Rcs-regulated genes that confer these phenotypes, we took advantage of our observation that RcsA, a transcription factor and binding partner of RcsB, is not required for polymyxin B resistance or survival in mice. S. enterica serovar Typhimurium oligonucleotide microarrays were used to identify 18 loci that are activated by RcsC, RcsD and RcsB but not RcsA. Five of the 18 loci encode genes that contribute to polymyxin B resistance. One of these genes, ydeI, was shown by quantitative real-time PCR to be regulated by the Rcs pathway independently of RcsA. Additionally, the stationary-phase sigma factor, RpoS (sigmaS), regulates ydeI transcription. In vivo infections show that ydeI mutants are out-competed by wild type 10-to 100-fold after oral inoculation, but are only modestly attenuated after intraperitoneal inoculation. These data indicate that ydeI is an Rcsactivated gene that plays an important role in persistent infection of mice, possibly by increasing bacterial resistance to antimicrobial peptides.

Genome Expression Analyses Revealing the Modulation of the Salmonella Rcs Regulon by the Attenuator IgaA

“…Important traits of serovar Typhimurium, such as its virulence potential, depend on the fine-tuning of the activity of the RcsCDB system (17,28,45). IgaA and the RcsCDB system are present in the same genera of enteric bacteria (17,20,34), and this concurrence strongly supports the functional link existing between IgaA and the RcsCDB system.…”

“…The Rcs regulon of Yersinia pseudotuberculosis has been estimated to be formed by at least 136 genes, with 60% of the genes encoding functions related to envelope homeostasis (31). In serovar Typhimurium, 26 RcsB-dependent but RcsA-independent genes were reported upon exposure of bacteria to sublethal concentrations of antimicrobial peptides (20). Recent studies performed with serovar Typhimurium expressing IgaA(T191P), a variant previously shown by us to be unable to repress the RcsCDB system (17), revealed that one-fifth of the genes analyzed displayed expression changes higher than twofold (55).…”

“…Most genes subjected to regulation by the RcsCDB system encode envelope proteins and factors related to the synthesis of diverse exopolysaccharides (20,22,23,27,30,35). It has been proposed that, upon sensing envelope alterations, bacteria activate the RcsCDB system to remodel the envelope composition accordingly.…”

“…A widely studied two-component signaling system is the RcsCDB signaling system, first identified in Escherichia coli as a regulator of the production of the colanic acid capsule (53). This system can be activated by diverse envelope-related stresses (13,14,19,20,35,36,47,49,52,61) or the overproduction of proteins such as DjlA, LolA, and OmpG (11,37).…”

Molecular Mechanisms Used by Salmonella to Evade the Immune System

“…Examples of these factors are PgtE, a modifier of the bacterial outer surface membrane (Lawley et al, 2006), and Mig-14, which provides resistance against anti-microbial peptides like VirK, RcsC, and YdeI (Erickson and Detweiler, 2006), both of them regulated by the PhoP/PhoQ system (Bader et al, 2005).…”