IgaA protein, GumB, has a global impact on the transcriptome and surface proteome of Serratia marcescens

Abstract

Bacterial stress response signaling systems, like the Rcs system, can be triggered by membrane and cell wall damaging compounds including antibiotics and innate immune system factors. These regulatory systems help bacteria survive envelope stress by altering the transcriptome resulting in protective phenotypic changes that may also the influence the virulence of the bacterium. This study investigated the role of the Rcs stress response system using a clinical keratitis isolate of S. marcescens with a mutation in the gumB gene. GumB, an IgaA ortholog, inhibits activation of the Rcs system, such that mutants have overactive Rcs signaling. Transcriptomic analysis indicated that approximately 15% of all S. marcescens genes were significantly altered with two-fold or greater changes in expression in the ΔgumB mutant compared to the wild type indicating a global transcriptional regulatory role for GumB. We further investigated the phenotypic consequences of two classes of genes with altered expression in the ΔgumB mutant expected to contribute to infections: serralysin metalloproteases PrtS, SlpB and SlpE, and type I pili coded by fimABCD. Secreted fractions from the ΔgumB mutant had reduced cytotoxicity to a corneal cell line, and could be complemented by induced expression of prtS, but not cytolysin shlBA, phospholipase phlAB, or flagellar master regulator flhDC operons. Proteomic analysis, qRT-PCR, and type I pili dependent yeast agglutination indicated an inhibitory role for the Rcs system in adhesin production. Together these data demonstrate that GumB and the Rcs stress response system control S. marcescens virulence factors beyond the ShlA cytolysin.IMPORTANCEPrevious studies indicate that the bacterial Rcs system is a key regulator of envelope stress. This study demonstrated that activation of the Rcs system had a global impact on the transcriptome of a clinical isolate of S. marcescens including decreased expression of cytotoxic serralysin metalloproteases and biofilm promoting type I pili. These results give mechanistic insight into how the Rcs system contributes to pathogenesis.

The short chain fatty acid propionic acid activates the Rcs stress response system partially through inhibition of D-alanine racemase

“…The bacterial flagellum is a potent activator of inflammation through binding with TLR5 (47). Flagellar genes are regulated by the Rcs system in numerous species including S. marcescens (19, 26). We tested whether physiologic concentrations of propionic acid had an impact on S. marcescens flagellum-based motility (Figure 7).…”

“…However, as Rcs activation promotes enhanced survival at near minimum inhibitory antibiotic concentrations, activation could increase persistence of bacteria in niches in the body with near inhibitory antibiotic levels that do not achieve sufficient levels to inactivate them (12). The Rcs system is also of interest as a regulator of virulence determinants including capsule, secreted toxins, flagella, and adhesion molecules (15)(16)(17)(18)(19). Generally, Rcs overactive mutants exhibit reduced virulence and those with defective Rcs systems demonstrate increased virulence (20)(21)(22).…”

“…S. marcescens is associated with microbial dysbiosis in Crohn’s disease (23) and is found in numerous environmental niches such as water, soil, plants, coral, and the gut flora of mammals and insects (24, 25). S. marcescens mutants with an inactivated or over-activated Rcs system demonstrate shifts in the global transcriptional landscape (19, 26). Other work has demonstrated a role for the Rcs system in regulation of S. marcescens virulence and virulence factors including the ShlA cytolysin (27).…”