Quorum Sensing Regulators Are Required for Metabolic Fitness in Vibrio parahaemolyticus.

Quorum sensing (QS) is a process by which bacteria alter gene expression in response to cell density changes. In 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 , a significant enteric pathogen of humans, the roles of these regulators in pathogenesis are less known. We examined deletion mutants of , , and for fitness using an adult mouse model. We found that the and mutants were defective in colonization compared to levels in the wild type. The mutant did not show any defect Colonization was restored to wild-type levels in a double mutant and was also increased in an double mutant. These data suggest that AphA is important and that overexpression of is detrimental to fitness. Transcriptome sequencing (RNA-Seq) analysis of the wild type and mutant grown in mouse intestinal mucus showed that 60% of the genes that were downregulated in the mutant were involved in amino acid and sugar transport and metabolism. These data suggest that the 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.