Quorum Sensing Regulators Are Required for Metabolic Fitness in Vibrio parahaemolyticus

Abstract

Quorum sensing (QS) is a process by which bacteria alter gene expression in response to cell density changes. In Vibrio species, at low cell density, the sigma 54-dependent response regulator LuxO is active and regulates the two QS master regulators AphA, which is induced, and OpaR, which is repressed. At high cell density the opposite occurs: LuxO is inactive, and therefore OpaR is induced while AphA is repressed. In Vibrio parahaemolyticus, a significant enteric pathogen of humans, the roles of these regulators in pathogenesis are less known. We examined deletion mutants of luxO, opaR, and aphA for in vivo fitness using an adult mouse model. We found that the luxO and aphA mutants were defective in colonization compared to levels in the wild type. The opaR mutant did not show any defect in vivo. Colonization was restored to wild-type levels in a luxO opaR double mutant and was also increased in an opaR aphA double mutant. These data suggest that AphA is important and that overexpression of opaR is detrimental to in vivo fitness. Transcriptome sequencing (RNA-Seq) analysis of the wild type and luxO mutant grown in mouse intestinal mucus showed that 60% of the genes that were downregulated in the luxO mutant were involved in amino acid and sugar transport and metabolism. These data suggest that the luxO mutant has a metabolic disadvantage, which was confirmed by growth pattern analysis using phenotype microarrays. Bioinformatics analysis revealed OpaR binding sites in the regulatory region of 55 carbon transporter and metabolism genes. Biochemical analysis of five representatives of these regulatory regions demonstrated direct binding of OpaR in all five tested. These data demonstrate the role of OpaR in carbon utilization and metabolic fitness, an overlooked role in the QS regulon.KEYWORDS Vibrio parahaemolyticus, carbon metabolism, intestinal colonization, quorum sensing V ibrio parahaemolyticus is the leading cause of bacterial seafood-borne gastroenteritis worldwide, resulting in mild to severe inflammatory gastroenteritis (1-5). The completed genome sequence of V. parahaemolyticus RIMD2210633, an O3:K6 serotype associated with pandemic disease, demonstrated the presence of two type III secretion systems (T3SS-1 and T3SS-2), one on each chromosome, which led to the identification of several effector proteins associated with inflammatory diarrhea (6-8). Studies have shown that T3SS-2 is the major contributing factor to enterotoxicity and that inflammatory diarrhea and intestinal epithelium cell disruption are dependent upon a functional T3SS-2 (9-12).Much less is known about how V. parahaemolyticus initially colonizes and survives within the host gastrointestinal tract. This lack of knowledge is in part due to a lack of animal models to study colonization and infection in vivo. The development of a streptomycin-pretreated adult mouse model that removes microbiota colonization resistance and allows V. parahaemolyticus to colonize has uncovered a number of

Quorum Sensing Gene Regulation by LuxR/HapR Master Regulators in Vibrios

“…A ΔluxO mutant exhibits significant fitness defects, while an ΔopaR mutant shows fitness advantages when grown on a variety of different carbon sources (e.g., glucose, gluconate, mannose, ribose, and arabinose). These results suggest that OpaR balances metabolic flux in V. parahaemolyticus in a manner similar to HapR in V. cholerae (99).…”

“…Quorum sensing via LitR activates the production of acetyl coenzyme A (acetyl-CoA) synthase (Acs), which converts acetate into acetyl-CoA and counteracts the acidification (98). In addition, the quorum sensing network in V. parahaemolyticus represses 64 genes associated with the transport and metabolism of amino acids, carbohydrates, and lipids (99). A ΔluxO mutant exhibits significant fitness defects, while an ΔopaR mutant shows fitness advantages when grown on a variety of different carbon sources (e.g., glucose, gluconate, mannose, ribose, and arabinose).…”

Quorum Sensing Regulators AphA and OpaR Control Expression of the Operon Responsible for Biosynthesis of the Compatible Solute Ectoine

“…Quorum sensing is a form of bacterial communication used to coordinate behaviors in response to changing cell density. The quorum sensing circuitry has been studied extensively in V. harveyi, and a similar system with a LuxR homologue, OpaR, has been demonstrated in V. parahaemolyticus (16)(17)(18)(19)(20)(21)(22). Quorum sensing involves the synthesis of autoinducers (AIs), which bind to receptors, triggering a phosphorelay pathway that activates LuxO, the master response regulator.…”

“…Previously, it was shown that LuxR in V. harveyi positively regulates glycine betaine biosynthesis genes (32). In V. parahaemolyticus, it was demonstrated that the ectoine biosynthesis genes were repressed in a luxO mutant (where OpaR levels are high) compared to the wild type (WT) (22).…”

L-ascorbic acid (vitamin C) fermentation by the human pathogenVibrio cholerae

“…Previous studies have shown that Vibrio species can utilize intestinal mucus as a carbon and energy source (25)(26)(27)(28). Therefore, we examined the expression pattern of the ula genes in V. cholerae cells growth in M9-Mucus.…”