Complex Control of a Genomic Island Governing Biofilm and Rugose Colony Development in Vibrio vulnificus

is a potent opportunistic human pathogen that contaminates the human food chain by asymptomatically colonizing seafood. The expression of the 9-gene exopolysaccharide locus mediates surface adherence and is controlled by the secondary signaling molecule c-di-GMP and the regulator BrpT. Here, we show that c-di-GMP and BrpT also regulate the expression of an adjacent 5-gene cluster that includes the operon, , and another VpsT-like transcriptional regulator gene, The expression of the 14 genes spanning the region increased with elevated intracellular c-di-GMP levels in a BrpT-dependent manner, save for , which was positively regulated by c-di-GMP and repressed by BrpT. BrpS repressed expression and was required for rugose colony development. The mutation of its consensus WFSA c-di-GMP binding motif blocked these activities, suggesting that BrpS function is dependent on binding c-di-GMP. BrpT specifically bound the , , and promoters, and binding sites homologous to the VpsT binding site were identified upstream of and Transcription was initiated distal to , and a conserved RfaH-recruiting element and a potential Rho utilization ( ) terminator site were identified within the 100-bp leader region, suggesting the integration of early termination and operon polarity suppression into the regulation of transcription. The GC content and codon usage of the 16-kb region was 5.5% lower relative to that of the flanking DNA, suggesting its recent assimilation via horizontal transfer. Thus, architecturally, the region can be considered an acquired biofilm and rugosity island that is subject to complex regulation. Biofilm and rugose colony formation are developmental programs that underpin the evolution of as a potent opportunistic human pathogen and successful environmental organism. A better understanding of the regulatory pathways governing theses phenotypes promotes the development and implementation of strategies to mitigate food chain contamination by this pathogen. c-di-GMP signaling is central to both pathways. We show that the molecule orchestrates the expression of 14 genes clustered in a 16-kb segment of the genome that governs biofilm and rugose colony development. This region exhibits the hallmarks of horizontal transfer, suggesting complex regulatory control of a recently assimilated genetic island governing the colonization response of .