Regulators of natural competence in Vibrio parahaemolyticus

Vibrio parahaemolyticus can degrade insoluble chitin with the help of chitinase enzymes that generate soluble N-acetyl glucosamine oligosaccharides (GlcNAc_n) to induce a state of natural competence for the uptake of extracellular DNA. In this study, we had evaluated the role of various regulatory factors such as TfoX, CytR, OpaR, and RpoS during natural transformation of V. parahaemolyticus. The results suggest that TfoX regulates natural competence via CytR in a chitin-dependent manner. CytR controls the release of GlcNAc₆ from insoluble chitin and conversion of GlcNAc₆ into smaller GlcNAc residues inside the periplasm by modulating the expression of endochitinase and periplasmic chitinases. In addition, CytR was also responsible for GlcNAc₆-mediated upregulation of competence-related genes such as pilA, pilB, comEA, and qstR. Next, we found that the quorum sensing regulator OpaR affects the natural transformation through its regulation of extracellular nuclease Dns. The ΔopaR mutant showed increased expression of Dns, which might degrade the eDNA. As a consequence, the transformation efficiency was decreased and eDNA-dependent growth was hugely enhanced. However, when Dns-containing DASW was substituted with fresh DASW, the transformation was detectable in ΔopaR mutant and eDNA-dependent growth was less. These results suggest that the occurrence of natural transformation and eDNA-dependent growth were inversely related to each other. Lastly, the general stress regulator RpoS was required for neither quorum-sensing dependent nor chitin-dependent regulation of natural competence in V. parahaemolyticus.