A novel Diguanylate cyclase VdcR has multifaceted regulatory functions in the pathogenicity of Vibrio vulnificus.

Background: Vibrio vulnificus is a Gram-negative pathogen that infects humans through foodborne or wound infections. Victims of V. vulnificus infections face significant health risks, including cellulitis and septicemia, which have rapid disease progression and high mortality rates. Diguanylate cyclase is responsible for producing the secondary messenger cyclic di-GMP. It plays a crucial role in regulating various bacterial physiological processes, such as motility, toxicity, and pathogenicity, through transcriptional regulation and affecting cyclic di-GMP levels. However, the DGC-mediated pathogenicity regulation in V. vulnificus is still unclear.

Methods: The vdcR gene in V. vulnificus was studied using a deletion strain (ΔVdcR) and an overexpression strain (oeVdcR) to understand its role in regulating the bacterium's pathogenicity. The electrophoretic mobility shift assay and RT-qPCR confirmed VdcR's impact on phosphodiesterase gene expression. To investigate how VdcR affects pathogenicity, V. vulnificus variant strains were assays for hemolysis, metalloprotease activity, cytotoxicity, resistance to phagocytosis, and lethality assays of the nematode Caenorhabditis elegans after infection.

Results: This study discovered a virulence-associated diguanylate cyclase, VdcR, which serves as a transcriptional regulator to induce phosphodiesterases and reduce the accumulation of cyclic di-GMP. VdcR expression resulted in low hemolysis, metalloprotease, and cytotoxicity activity. It also improved the cell adhesion ability and anti-phagocytosis activity to infect the host cell and escape the macrophage phagocytosis. The constitutively expressed VdcR in V. vulnificus caused low mortality rates in Caenorhabditis elegans survival assays.

Conclusion: The above evidence demonstrated that VdcR suppresses the pathogenicity in V. vulnificus YJ016.