The diguanylate cyclase and phosphodiesterase locally regulate the virulence factors in Vibrio vulnificus

Vibrio vulnificus is a marine pathogen that is a significant cause of foodborne infections, leading to chronic diseases and primary septicemia. Wound infections caused by this bacterium can result in serious complications such as ulceration and tissue necrosis. The pathogenesis of V. vulnificus is influenced by quorum sensing and the secondary messenger cyclic diguanylate (c-di-GMP). The levels of c-di-GMP inside the cell are controlled by its synthesizer, diguanylate cyclase, and its degrader, phosphodiesterase. The phosphodiesterase VieA serves as a key transcriptional regulator in V. cholerae's virulence. However, the function of its diguanylate cyclase partner in locally controlling c-di-GMP-mediated virulence regulation in V. vulnificus remains unclear. This study identified a diguanylate cyclase, VV2380, which may interact with VieA in V. vulnificus based on a pulldown assay. The enzymatic properties of VV2380 showed that it is a metal ion-dependent diguanylate cyclase that synthesizes c-di-GMP. Activity tests demonstrated that reversible phosphorylation on residue D207 of VV2380 regulates GTP hydrolysis activity to increase c-di-GMP levels. The elevated c-di-GMP level mediated by VV2380 results in rugose colony morphology and reduced motility, but does not influence biofilm formation. The VV2380-VieA signaling network significantly suppressed the gene expression levels of vvpE and rtxA1, reducing cytolysin activity and Multifunctional-Autoprocessing Repeats-in-Toxin (MARTX) production, which led to lower cytotoxicity toward host cells. In summary, this study highlights that diguanylate cyclase VV2380 and phosphodiesterase VieA are part of a local c-di-GMP signaling network that modulates the phenotypic features and the pathogenesis. It offers a new explanation for how various diguanylate cyclases and phosphodiesterases in V. vulnificus regulate different responses.