CqsA-introduced quorum sensing inhibits type VI secretion system 2 through an OpaR-dependent pathway in Vibrio parahaemolyticus.

The well-known food-borne pathogen Vibrio parahaemolyticus employs at least three quorum sensing signals to maintain its high environmental adaptability. V. parahaemolyticus CqsA, the synthase involved in 3-hydroxyundecan-4-one quorum sensing signal, introduces a quorum sensing network. The V. parahaemolyticus virulent factor type VI secretion system 2 (T6SS2), which is associated with adhesion to host cells, was previously reported to be regulated by a quorum sensing system. Herein, we set out to determine the role of CqsA-introduced quorum sensing (CIQS) in T6SS2-associated virulent regulation. Using a tandem mass tag (TMT)-based quantitative proteomics assay, 17 T6SS2 proteins were found having significantly higher abundances in the ΔcqsA strain than in the wild type strain. TMT proteomics assay results were confirmed by a parallel reaction-monitoring (PRM)-based proteomics assay. Two T6SS2 up-regulators, OpaR and CalR, were found under control of CIQS in the TMT proteomics assay, while OpaR was down-regulated and CalR was up-regulated by CIQS. Thus, it was hypothesized that CIQS would inhibit T6SS2 with an OpaR-dependent mechanism. Epistasis experiment with quantitative PCR was designed to analyze the role of OpaR in the process of CIQS inhibiting T6SS2 production. The mRNA levels of T6SS2 genes were up-regulated in the ΔcqsA strain while down-regulated in the ΔopaR strain and in the ΔcqsAΔopaR mutant, indicating that OpaR plays a predominant role in the regulation of T6SS2 by CIQS. Using a cell adhesion assay, we further found that the T6SS2-dependent adhesion activity of V. parahaemolyticus to Hela cells was also inhibited by CIQS and the inhibition was OpaR-dependent. In this study, we confirmed that V. parahaemolyticus CIQS inhibited T6SS2 through an OpaR-dependent pathway. It enriches the knowledge of how V. parahaemolyticus quorum sensing regulates its virulence.

[Virulence-associated gene detection and ERIC-PCR typing of Campylobacter jejuni strains isolated from foods in four Southern Chinese provinces].

OBJECTIVE: To know food contamination and genetic diversity of Campylobacter jejuni in four provinces of South China, and to provide data for C. jejuni-associated foodborne disease prevention and control. METHODS: According to the national standard and the most probable number (MPN) method, we detected the contamination of C. jejuni from 558 food samples including vegetables, meat product, cooked food, seafood, frozen food, dairy product and edible fungi during 2011 and 2012. The isolates were used to detect 12 virulence-associated genes with PCR methods and construct ERIC-PCR fingerprints. RESULTS: Fourteen positive samples were determined from 558 samples, and all positive samples come from meat product samples. The average value of MPN of positive samples was 8.77 MPN/g. Virulence-associated gene analysis reveals that more than 50% of the C. jejuni isolates had at least 9 virulence genes. Interestingly, virB11 gene was not found and the genes of pldA and wlaN were 14.30% in all isolates. Total of 15 C. jejuni isolates could be divided into 10 genotypes belonging to 3 clusters by ERIC-PCR fingerprints. CONCLUSION: Meat product was the main source of C. jejuni food contamination in four provinces of South China. More control measures must be taken to avoid C. jejuni contamination.

Erratum to: Vibrio parahaemolyticus cqsA controls production of quorum sensing signal molecule 3-hydroxyundecan-4-one and regulates colony morphology.

In the article by Wu et al. published in Journal of Microbiology 2019; 57, 1105-1114, the figure 8 is unfortunately incorrect. The figure 8 should be corrected as below.

Vibrio parahaemolyticus cqsA controls production of quorum sensing signal molecule 3-hydroxyundecan-4-one and regulates colony morphology.

In order to adapt to different environments, Vibrio parahaemolyticus employed a complicated quorum sensing system to orchestrate gene expression and diverse colony morphology patterns. In this study, the function of the putative quorum sensing signal synthase gene cqsA (VPA0711 in V. Parahaemolyticus strain RIMD2210633 genome) was investigated. The cloning and expression of V. parahaemolyticus cqsA in Escherichia coli system induced the production of a new quorum sensing signal that was found in its culture supernatant. The signal was purified by high performance liquid chromatography methods and determined to be 3-hydroxyundecan- 4-one by indirect and direct mass spectra assays. The deletion of cqsA in RIMD2210633 changed V. parahaemolyticus colony morphology from the classical 'fried-egg' shape (thick and opaque in the center, while thin and translucent in the edge) of the wild-type colony to a 'pancake' shape (no significant difference between the centre and the edge) of the cqsA deleted colony. This morphological change could be restored by complementary experiment with cqsA gene or the signal extract. In addition, the expression of opaR, a well-known quorum sensing regulatory gene, could be up-regulated by cqsA deletion. Our results suggested that V. parahaemolyticus used cqsA to produce 3-hydroxyundecan-4-one signal and thereby regulated colony morphology and other quorum sensing-associated behaviors.