PhD Dissertation Defense: Lauren Speare

The PhD Dissertation Defense of Lauren Speare is presented by the University of North Carolina at Chapel Hill’s Department of Marine Sciences. This event will be held on Thursday, March 25th at 11:00 am. This event will be held ONLINE ONLY and it will be available online via Zoom Meeting ID 940 8168 2024

Title: Ecology of type VI secretion competition in the beneficial bacterial symbiont Vibrio fischeri

Abstract: Microbial communities perform vital ecosystem functions that impact host health and drive essential biogeochemical processes on our planet. These communities, however, do not always assemble peacefully and bacteria have evolved diverse strategies to eliminate competitors. One such mechanism is the type VI secretion system (T6SS), a contact-dependent killing mechanism found broadly-distributed among both beneficial and pathogenic species. Despite the prevalence of T6SSs in host microbiomes, few studies have investigated their ecological roles because they are often challenging to study in situ due to the inherent complexity of host-associated communities. This dissertation uses the relationship between the marine bacterium Vibrio fischeri and Euprymna scolopes squid as a simplified model for studying bacterial competition during symbiosis establishment. Using novel in vitro and in vivo assays I demonstrate that V. fischeri contain a strain-specific T6SS that is used to spatially structure the microbial population within a natural host early during colonization. I developed culture conditions that mimic the physical environment within host tissue to characterize the host-specific signals that modulate T6SS competition during habitat transition, and identify a mechanism for T6SS+ cells to discriminate between potential competitor cells. This dissertation provided new tools to examine bacterial behaviors that may be relevant in a host, yet are difficult to study using traditional culturing methods and laid the foundation for the Vibrio-squid symbiosis as a powerful system to probe molecular mechanisms of interbacterial competition during natural host colonization.