MS Thesis Defense: Stephanie Smith

UNC-CH’s Department of Marine Sciences is proud to announce the Master’s Thesis Defense of Stephanie Smith. This event is scheduled for Wednesday, October 28th, at 12:30 pm. This seminar is remote only and will be broadcast live online via Zoom (Meeting ID: 991-4917-3565).

Presenter Affiliation: Graduate Student, Septer Lab Member, Department of Marine Sciences, University of North Carolina at Chapel Hill

Title: The Role of Chromosomal DNA Exchange and Bacterial Evolution in the Squid Symbiont, Vibrio fischeri

Abstract: Animals evolved surrounded by bacteria, resulting in widespread symbioses in which host and symbiont often form specialized partnerships that are essential for host development, reproduction, or survival. Specific genes are often required for bacteria to colonize a given host, and it is predicted that these genetic factors can be rapidly transferred between bacteria through the exchange of genetic material (gene transfer). However, little is known about the effect of gene transfer on the ability of bacteria to acquire colonization factors that permit them to colonize new hosts. We used coincubations between different isolates of the bioluminescent light organ symbiont, Vibrio fischeri, to quantify and characterize the role of gene exchange in the evolution of symbiotic partnerships. In this study, we evolved a fish symbiont by growing it in the presence of a squid symbiont that can transfer DNA into other bacterial cells. Comparative genomics of five representative evolved fish symbionts revealed that (1) the evolved isolates acquired genomic DNA from the squid isolate, and (2) that this DNA was transferred using a mechanism that has not yet been described for V. fischeri. Exposing juvenile Hawaiian bobtail squid to a pool of evolved fish symbionts revealed that some fish symbionts had gained the ability to colonize the squid host. Taken together, these findings suggest that V. fischeri is able to rapidly evolve through a previously undescribed mechanism of DNA transfer to colonize new hosts, and underscores the importance of using the squid-vibrio symbiosis as a model system to study natural mechanisms for the evolution of bacterial genomes and symbiotic partnerships.