The Sensor Histidine Kinase RgfC Affects Group B Streptococcal Virulence Factor Expression Independent of Its Response Regulator RgfA

Abstract

Group B streptococci (GBS; Streptococcus agalactiae) are beta-hemolytic, Gram-positive bacteria that are common asymptomatic colonizers of healthy adults. However, these opportunistic bacteria also cause invasive infections in human newborns and in certain adult populations. To adapt to the various environments encountered during its disease cycle, GBS encodes a number of two-component signaling systems. Previous studies have indicated that the TCS comprising the sensor histidine kinase RgfC and the response regulator RgfA mediate GBS binding to extracellular matrix components, such as fibrinogen. However, in certain GBS clinical isolates, a point mutation in rgfA results in premature truncation of the response regulator. The truncated RgfA protein lacks the C-terminal DNA binding domain necessary for promoter binding and gene regulation. Here, we show that deletion of rgfC in GBS strains lacking a functional RgfA increased systemic infection. Furthermore, infection with the rgfC mutant increased induction of proinflammatory signaling pathways in vivo. Phosphoproteomic analysis revealed that 19 phosphopeptides corresponding to 12 proteins were differentially phosphorylated at aspartate, cysteine, serine, threonine, or tyrosine residues in the rgfC mutant. This included aspartate phosphorylation of a tyrosine kinase, CpsD, and a transcriptional regulator. Consistent with this observation, microarray analysis of the rgfC mutant indicated that >200 genes showed altered expression compared to the isogenic wild-type strain and included transcriptional regulators, transporters, and genes previously associated with GBS pathogenesis. Our observations suggest that in the absence of RgfA, nonspecific RgfC signaling affects the expression of virulence factors and GBS pathogenesis.A ll living organisms sense and adapt to dynamic changes in their environment using signaling systems. Signaling in prokaryotic organisms is achieved primarily by two-component signaling systems (TCS) that regulate gene expression in response to environmental signals (1-5). A typical two-component system comprises a membrane-associated sensor histidine kinase that responds to an environmental signal and phosphorylates its cognate DNA binding response regulator at an aspartate residue. Phosphorylation often alters the affinity of the response regulator to its target promoters, regulating gene expression.Group B streptococci (GBS) or Streptococcus agalactiae strains are a common cause of bacterial infections in human newborns and are emerging pathogens of adult humans (6). These bacteria reside as commensal organisms in the lower gastrointestinal and genital tracts of healthy adult women. Human neonates are at risk for GBS infections due to ascending infection from the lower genital tract or from aspiration of contaminated amniotic/vaginal fluids during birth. GBS can disseminate into multiple neonatal organs, causing pneumonia, sepsis, and meningitis (for reviews, see references 6-8). Thus, GBS has to efficiently adapt to the changing environmental...

Virulence regulation of cel‐EIIB protein mediated PTS system in Streptococcus agalactiae in Nile tilapia

“…RgfA/C regulated the transcription of fbsA and fbsB genes and mediated the binding with the host extracellular matrix fibrinogen, thus participating in the regulation of the adhesion and invasion of GBS to the host cells (Safadi et al., ). Gendrin confirmed that the pathogenicity of rgfC natural deletion mutants was increased, and the ability to infect the brain and spleen tissues of mice increased and the virulence enhanced (Gendrin et al., ). While, in this case, the expression of rgfC of △cel‐EIIB::i strain was significant up‐regulated.…”

“…The means and standard deviations (mean ± SD) for data were from three independent experiments. Statistical significance of mean values was assessed by a two-tailed Student's t test using SPSS 19.0 software (Gendrin et al, 2015). While, in this case, the expression of rgfC of △cel-EIIB::i strain was significant up-regulated.…”

Contribution of the RgfD Quorum Sensing Peptide to rgf Regulation and Host Cell Association in Group B Streptococcus

“…Because the rgf operon was found to facilitate binding to host cell components and impact virulence in vivo, [ 22 , 23 , 29 ] we sought to better understand the role of the putative autoinducing peptide, RgfD, in phenotypes important for colonization. Similar to prior studies [ 29 , 39 ], we have demonstrated rgf -dependent expression of the rgf operon and have identified genetic variation in the rgf operon genes among a diverse set of GBS strains. The large 881 bp deletion within rgfC is notable given that it was present in almost half of the 40 strains recovered from women with asymptomatic GBS colonization.…”

“…Mutations conferring a non-hemolytic, non-invasive phenotype have been detected in the agr operon from strains recovered from patients [ 24 , 28 ]. For the rgf operon, one study identified a truncation in the gene encoding the response regulator, rgfA , in several clinical strains and deletion of both rgfC , the sensor histidine kinase, and rgfA resulted in increased virulence in a mouse and rat model [ 29 ]. This increase was possibly due to other virulence mechanisms including increased sialic acid production and capsule operon transcription, which were both altered in the deletion mutant.…”

“…This increase was possibly due to other virulence mechanisms including increased sialic acid production and capsule operon transcription, which were both altered in the deletion mutant. The same study also found that extrachromosomal rgfC expression altered the transcriptome, indicating that regulation of the sensor histidine kinase may be important for GBS pathogenesis [ 29 ]. Separate analyses of the genome of NEM316, a serotype III ST-23 GBS strain isolated from a fatal case of neonatal septicemia, also identified a large deletion within rgfD , which encodes a putative auto-inducing peptide, and part of rgfC [ 30 ].…”