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.

KEYWORDS:

• Type VI secretion system (T6SS)
• quorum sensing (QS)
• LuxO
• HapR
• Vibrio fluvialis

Acknowledgements

The authors thank Dr Jingyun Zhang for suggestions in statistical interpretation of data and members in Branch of Diarrheal Diseases (ICDC) for technical help and discussion. The opinions, conclusions, and recommendations in this report are those of the authors and do not necessarily represent the official positions of the National Institute for Communicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention (ICDC).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study is supported by grants from the National Natural Science Foundation of China (81772242), and the National Science and Technology Major Project (2018ZX10713-003-002-009).