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...
SummaryVibrio cholerae live in aquatic environments and cause cholera disease. Like many other bacteria, V. cholerae use quorum-sensing (QS) systems to control various cellular functions, such as pathogenesis and biofilm formation. However, some V. cholerae strains are naturally QSdefective, including defective mutations in the quorum sensing master regulator HapR. Here we examined the QS functionality of 602 V. cholerae clinical and environmental strains isolated in China from 1960-2007, by measuring QS-regulated gene expression. We found that a greater percentage of the toxigenic strains (ctxAB + ) had functional QS as compared to the non-toxigenic strains (ctxAB − ), and that this trend increased significantly over time. We hypothesize that QS provides adaptive value in V. cholerae pathogenic settings.
dVibrio fluvialis is an important food-borne pathogen that causes diarrheal illness and sometimes extraintestinal infections in humans. In this study, we sequenced the genome of a clinical V. fluvialis strain and determined its phylogenetic relationships with other Vibrio species by comparative genomic analysis. We found that the closest relationship was between V. fluvialis and V. furnissii, followed by those with V. cholerae and V. mimicus. Moreover, based on genome comparisons and gene complementation experiments, we revealed genetic mechanisms of the biochemical tests that differentiate V. fluvialis from closely related species. Importantly, we identified a variety of genes encoding potential virulence factors, including multiple hemolysins, transcriptional regulators, and environmental survival and adaptation apparatuses, and the type VI secretion system, which is indicative of complex regulatory pathways modulating pathogenesis in this organism. The availability of V. fluvialis genome sequences may promote our understanding of pathogenic mechanisms for this emerging pathogen. Vibrio fluvialis is a Gram-negative, oxidase-producing, halophilic bacterium that is normally found in coastal water and seafood. Clinically, V. fluvialis has been implicated as a cause of gastroenteritis with diarrhea (1) and even wound infection with primary septicemia in immunocompromised individuals (2). In an epidemic situation, V. fluvialis behaved more aggressively than Vibrio cholerae O1, having a higher attack rate and a different clinical picture in the population (3). The gastrointestinal illness caused by this pathogen is usually associated with the consumption of raw or improperly cooked seafood. Additionally, this bacterium causes significant economic loss, like in the lobster industries of the eastern coasts of the United States and Canada (4). Therefore, V. fluvialis has gained importance as an epidemic-causing Vibrio, especially in coastal areas.V. fluvialis was broadly defined as a nonagglutinating Vibrio species (5). It was first isolated in 1975 from patients with severe diarrhea (6) and was originally called "group F Vibrios" by Furniss et al. and "EF-6 Vibrios" by the Centers for Disease Control (6, 7). Both phenotypic tests and DNA relatedness indicated that these organisms were much closer to the genus Vibrio than to the genus Aeromonas (8). In some taxonomic studies, group F was separated into two subgroups based on gas production during glucose fermentation (9, 10). The aerogenic group F strains were in a different DNA relatedness group from the anaerogenic strains, and the two biogroups were separated into two species within the genus Vibrio (8). The name V. fluvialis was proposed for both aerogenic and anaerogenic strains of group F and the synonymous group EF-6. However, only anaerogenic strains have been isolated from human samples, even though both aerogenic and anaerogenic strains of V. fluvialis have been found in the environment (11). Subsequently, the aerogenic strains of group F were confirmed to be...
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