VanT, a Homologue of Vibrio Harveyi LuxR, Regulates Serine, Metalloprotease, Pigment, and Biofilm Production in Vibrio Anguillarum

Vibrio anguillarum possesses at least two N-acylhomoserine lactone (AHL) quorum-sensing circuits, one of which is related to the luxMN system of Vibrio harveyi. In this study, we have cloned an additional gene of this circuit, vanT, encoding a V. harveyi LuxR-like transcriptional regulator. A V. anguillarum Delta vanT null mutation resulted in a significant decrease in total protease activity due to loss of expression of the metalloprotease EmpA, but no changes in either AHL production or virulence. Additional genes positively regulated by VanT were identified from a plasmid-based gene library fused to a promoterless lacZ. Three lacZ fusions (serA::lacZ, hpdA-hgdA::lacZ, and sat-vps73::lacZ) were identified which exhibited decreased expression in the Delta vanT strain. SerA is similar to 3-phosphoglycerate dehydrogenases and catalyzes the first step in the serine-glycine biosynthesis pathway. HgdA has identity with homogentisate dioxygenases, and HpdA is homologous to 4-hydroxyphenylpyruvate dioxygenases (HPPDs) involved in pigment production. V. anguillarum strains require an active VanT to produce high levels of an L-tyrosine-induced brown color via HPPD, suggesting that VanT controls pigment production. Vps73 and Sat are related to Vibrio cholerae proteins encoded within a DNA locus required for biofilm formation. A V. anguillarum Delta vanT mutant and a mutant carrying a polar mutation in the sat-vps73 DNA locus were shown to produce defective biofilms. Hence, a new member of the V. harveyi LuxR transcriptional activator family has been characterized in V. anguillarum that positively regulates serine, metalloprotease, pigment, and biofilm production.