Quorum Sensing Regulatory Cascades Control Vibrio fluvialis Pathogenesis

Abstract

c Quorum sensing (QS) is a process by which individual bacteria are able to communicate with one another, thereby enabling the population as a whole to coordinate gene regulation and subsequent phenotypic outcomes. Communication is accomplished through production and detection of small molecules in the extracellular milieu. In many bacteria, particularly Vibrio species, multiple QS systems result in multiple signals, as well as cross talk between systems. In this study, we identify two QS systems in the halophilic enteric pathogen Vibrio fluvialis: one acyl-homoserine lactone (AHL) based and one CAI-1/AI-2 based. We show that a LuxI homolog, VfqI, primarily produces 3-oxo-C10-HSL, which is sensed by a LuxR homolog, VfqR. VfqR-AHL is required to activate vfqI expression and autorepress vfqR expression. In addition, we have shown that similar to that in V. cholerae and V. harveyi, V. fluvialis produces CAI-1 and AI-2 signal molecules to activate the expression of a V. cholerae HapR homolog through LuxO. Although VfqR-AHL does not regulate hapR expression, HapR can repress vfqR transcription. Furthermore, we found that QS in V. fluvialis positively regulates production of two potential virulence factors, an extracellular protease and hemolysin. QS also affects cytotoxic activity against epithelial tissue cultures. These data suggest that V. fluvialis integrates QS regulatory pathways to play important physiological roles in pathogenesis. Bacteria often exchange chemical signals to help them monitor their population densities through a phenomenon referred to as quorum sensing (QS) (1). The genus Vibrio includes more than 30 species, many of which are associated with human diseases, and have described QS systems for both interbacterial and intrabacterial communication (2). Among them, the acyl-homoserine lactone (AHL) system in Vibrio fischeri is well characterized and is used as a model system for many AHL-producing Gram-negative bacteria (3). The AHL signal molecule is produced by the AHL synthase LuxI and recognized by the LuxR receptor, leading to altered gene expression of downstream genes. In Vibrio cholerae, the causative agent of cholera (4), the major QS signal molecules are 3-hydroxytridecan-4-one (cholerae autoinducer-1 [CAI-1]) and AI-2 (5). Changes in these autoinducer levels correspond to repression or derepression of the major QS regulator, HapR. At a low cell density and signal concentration, a phosphorelay system is active, resulting in the phosphorylation of the terminal acceptor LuxO, a DNA-binding response regulator protein. PhosphoLuxO, together with a sigma factor 54 , activates transcription of the genes encoding a set of small RNAs that, in conjunction with RNA chaperone, Hfq, bind to and destabilize the transcript of HapR, the master QS regulator (6). Alternatively, at high cell density, QS molecules interact with their cognate sensors, leading to the dephosphorylation of LuxO. Consequently, LuxO is inactivated and HapR is expressed (7, 8; see also two review articles [9,10] for additional de...

Functional Characterization and Conditional Regulation of the Type VI Secretion System in Vibrio fluvialis

“…Our previous study demonstrated that VFH contributes to the pathogenicity of V. fluvialis by inducing IL-1β secretion through the activation of the NLRP3 inflammasome (Song et al, 2015). We also showed that quorum sensing in V. fluvialis positively regulates the production of hemolysin and extracellular protease and affects the cytotoxic activity against epithelial tissue cultures (Wang et al, 2013). …”

Complete genome sequencing ofPandoraea pnomenusaRB38 and Molecular Characterization of ItsN-acyl homoserine lactone synthase geneppnI

“…2 and 3 ). Moreover , all three QS genes of P. pnomenusa RB38 exhibit low sequence similarity (less than 50%) to any previously characterised LuxI/LuxR homologues, namely BpsI (protein ID: AAQ90168.1) ( Song et al, 2005 ); BpsI (protein ID: AAM21707.2) ( Lumjiaktase et al, 2006 ); BmuR (Protein ID: AAK50054.2) ( Yao, Zhou & Lessie, 2002 ); CepR (Protein ID: AAK70347.1) ( Lutter et al, 2001 ); NmuR (Protein ID: AHB23331.1) ( Gao et al, 2014 ); and VfqR (Protein ID: AGE97288.1) ( Wang et al, 2013 ). This suggests that the QS genes of P. pnomenusa RB38 represent a new evolutionary branch of the QS system and can potentially have novel regulatory roles.…”

A critical role for hemolysin in Vibrio fluvialis-induced IL-1β secretion mediated by the NLRP3 inflammasome in macrophages

“…SRX397301 ( Lu et al, 2014 ). The Δ vfh was constructed as previously described using allele replacement strategies ( Wang et al, 2013 ). To construct the pUC- vfh , a chromosomal DNA fragment comprising the vfh open reading frame and its promoter sequence was amplified with the primer pair 5′-CGG AAT TCT AAG ATC ATG TCT GAA TGT-3′/5′-CGG GAT CCC GAC TGA GTT CAG CTC TCA C-3′.…”

“…Cell-free culture filtrates of V. fluvialis strains are able to evoke distinct cytotoxic and vacuolization effects on HeLa cells ( Chakraborty et al, 2005 ). Quorum sensing in V. fluvialis positively regulates production of an extracellular protease and hemolysin and affects cytotoxic activity against epithelial tissue cultures ( Wang et al, 2013 ). Of note, the V. fluvialis- caused diarrhea with presence of blood is different from cholera.…”