Project description:Beneficial microbial symbionts are often horizontally acquired by their animal hosts from environmental sources, requiring the symbionts to complete a lifestyle transition from free-living in the environment to association with host tissues. In the model symbiosis between the Hawaiian bobtail squid and its microbial symbiont Vibrio fischeri, one mechanism used to make this transition during host colonization is the formation of biofilm-like aggregates on host mucosa. Extensive work has previously been conducted to isolate the critical factors controlling V. fischeri biofilm formation, yet much remains unknown regarding the full breadth of the biofilm-associated regulon. Here, we probed in vitro models of biofilm formation using transcriptomics, to identify novel regulatory pathways active within biofilms of the V. fischeri type strain ES114. Through comparing the gene-sets which became differentially regulated in multiple biofilm models, we discovered a shared set of 232 genes which demonstrated similar patterns in expression relative to uninduced controls. These genes contained representatives of multiple exopolysaccharide loci, genes involved in flagellar motility, and a diverse collection of other genes. Follow-up analysis suggested that these transcriptomic changes reflected true phenotypic effects, including changes in motility and cyclic-di-GMP production in biofilm-induced backgrounds. Beyond characterizing the shared biofilm response, we additionally profiled the regulatory activity of the sensor kinase RscS. This sensor kinase has previously been characterized to function as a phospho-donor within an established biofilm-inducing phospho-relay, yet our data suggests that RscS moonlights in at least one other phospho-relay that integrates downstream signaling from a homolog of the Vibrio cholerae response regulator VpsR, without a need for its established signaling partners. Overall, this study adds to our understanding of the genes involved in V. fischeri biofilm regulation, while revealing new regulatory pathways branching from previously characterized signaling networks.

Project description:The bioluminescent bacterium Vibrio fischeri forms a mutually beneficial symbiosis with the Hawaiian bobtail squid, Euprymna scolopes, in which the bacteria, housed inside a specialized light organ, produce light used by the squid in its nocturnal activities. Upon hatching, E. scolopes juveniles acquire V. fischeri from the seawater through a complex process that requires, among other factors, chemotaxis by the bacteria along a gradient of N-acetylated sugars into the crypts of the light organ, the niche in which the bacteria reside. Once inside the light organ, V. fischeri transitions into a symbiotic, sessile state in which the quorum-signaling regulator LitR induces luminescence. In this work we show that expression of litR and luminescence are repressed by a homolog of the V. cholerae virulence factor TcpP, which we have named HbtR. Further, we demonstrate that LitR represses genes involved in motility and chemotaxis into the light organ and activates genes required for exopolysaccharide production. Importance: TcpP homologs are widespread throughout the Vibrio genus; however, the only protein in this family described thus far is a V. cholerae virulence regulator. Here we show that HbtR, the TcpP homolog in V. fischeri, has both a biological role and regulatory pathway completely unlike that in V. cholerae. Through its repression of the quorum-signaling regulator LitR, HbtR affects the expression of genes important for colonization of the E. scolopes light organ. While LitR becomes activated within the crypts, and upregulates luminescence and exopolysaccharide genes and downregulates chemotaxis and motility genes, it appears that HbtR, upon expulsion of V. fischeri cells into seawater, reverses this process to aid the switch from a symbiotic to a planktonic state. The possible importance of HbtR to the survival of V. fischeri outside of its animal host may have broader implications for the ways in which bacteria transition between often vastly different environmental niches.

Dataset Information

Vibrio phage HNL01

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