Quorum Sensing Regulatory Cascades Control Vibrio fluvialis Pathogenesis

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, particularlyVibrio 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 pathogenVibrio 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 activatevfqI expression and autorepressvfqR expression. In addition, we have shown that similar to that inV. cholerae andV. harveyi ,V. fluvialis produces CAI-1 and AI-2 signal molecules to activate the expression of aV. cholerae HapR homolog through LuxO. Although VfqR-AHL does not regulatehapR expression, HapR can repressvfqR transcription. Furthermore, we found that QS inV. 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 thatV. fluvialis integrates QS regulatory pathways to play important physiological roles in pathogenesis.