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CqsA/LuxS-HapR Quorum sensing circuit modulates type VI secretion system VﬂT6SS2 in Vibrio fluvialis.

ABSTRACT: Vibrio fluvialis is an emerging enteric pathogen of increasing public health threat. Two quorum sensing (QS) systems, VfqI-VfqR and CqsA/LuxS-HapR, and two type VI secretion systems (T6SSs), VflT6SS1 and VflT6SS2, have been identified in V. fluvialis. Whether there exists any correlation between the two systems is unclear. In this study, we found that CqsA/LuxS-HapR circuit regulator LuxO represses while HapR activates VﬂT6SS2. The effect of LuxO is more pronounced at low cell density and is HapR-dependent. Deletion of hapR abolished Hcp expression and alleviated antibacterial virulence. However, these effects were rescued by HapR-expressing plasmid. Reporter fusion analyses showed that HapR is required for the promoter activities of VﬂT6SS2. Sequence inspection of the major cluster promoter revealed two potential Motif 1 HapR binding sites, and their bindings to HapR were confirmed by both electrophoretic mobility shift assay (EMSA) and DNase I footprinting assay. Meanwhile, two single Motif 2 sites were identified in tssD2_a (hcpA) and tssD2_b (hcpB) promoter regions of the orphan cluster which are less conserved and displayed lower affinities to HapR. Together, our study demonstrated that CqsA/LuxS-HapR QS manipulate VflT6SS2 in V. fluvialis, and this finding will enhance our understanding of possible crosstalk between T6SS and QS in microbes.

SUBMITTER: Liu X

PROVIDER: S-EPMC8018390 | biostudies-literature |

REPOSITORIES: biostudies-literature

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VfqI-VfqR quorum sensing circuit modulates type VI secretion system VflT6SS2 in <i>Vibrio fluvialis</i>.

Project description:V. fluvialis is an emerging foodborne pathogen and could cause cholera-like gastroenteritis syndrome and poses a potential threat to public health. VflT6SS2 is a functionally active type VI secretion system (T6SS) in V. fluvialis which confers bactericidal activity. VflT6SS2 is composed of one major cluster and three hcp-vgrG orphan clusters. Previously, we identified two quorum sensing (QS) systems CqsA/LuxS-HapR and VfqI-VfqR in V. fluvialis and demonstrated that the former regulates VflT6SS2. However, whether VfqI-VfqR QS regulates VflT6SS2 is unknown. In this study, we showed that the mRNA abundances of VflT6SS2 tssD2 (hcp), tssI2 (vgrG) and tssB2 (vipA) were all significantly decreased in VfqI or/and VfqR deletion mutant(s). Consistently, Hcp expression/secretion was reduced too in these mutants. Complementation assay with VfqR mutant further confirmed that the reduced Hcp expression/secretion and impaired antibacterial virulence are restored by introducing VfqR-expressing plasmid. Reporter fusion analyses revealed that VfqR modulates the promoter activities of VflT6SS2. Bioinformatical prediction and further reporter fusion assay in E. coli supported that VfqR acts as a transcriptional factor to bind and regulate the gene expression of the VflT6SS2 major cluster. However, VfqR seems to promote transcription of hcp (tssD2) in the orphan clusters through elevating the expression of vasH which is encoded by the VflT6SS2 major cluster. Additionally, we found that the regulation intensity of VfqR on VflT6SS2 is weaker than that of HapR. In conclusion, our current study disclosed that in V. fluvialis, VfqI-VfqR circuit upregulates the expression and function of VflT6SS2 by directly or indirectly activating its transcription. These findings will enhance our understanding of the complicated regulatory network between QS and T6SS in V. fluvialis.

| S-EPMC9166416 | biostudies-literature

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Crystal structure of the Vibrio cholerae quorum-sensing regulatory protein HapR.

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| S-EPMC1951804 | biostudies-literature

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| S-EPMC3285556 | biostudies-literature

The Vibrio cholerae quorum-sensing autoinducer CAI-1: analysis of the biosynthetic enzyme CqsA.

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| S-EPMC2847429 | biostudies-literature

Cell density- and quorum sensing-dependent expression of type VI secretion system 2 in Vibrio parahaemolyticus.

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Quorum sensing control of Type VI secretion factors restricts the proliferation of quorum-sensing mutants.

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Quorum sensing and a global regulator TsrA control expression of type VI secretion and virulence in Vibrio cholerae.

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Quorum regulatory small RNAs repress type VI secretion in Vibrio cholerae.

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| S-EPMC4038675 | biostudies-literature

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