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Research Seminar: Lauren Speare
February 26, 2018 @ 12:20 pm - 1:20 pm
A research seminar from UNC Marine Sciences graduate student, Lauren Speare. Presented by the UNC-CH Department of Marine Sciences and UNC’s Institute of Marine Sciences (IMS). The main location of this event will be in seminar room G201 on the ground floor of Murray Hall on UNC-CH campus in Chapel Hill, NC. The seminar will be streamed live to room 222 at IMS in Morehead City, NC. This event will be held on Monday, February 26th at 12:20pm.
Seminar Title: Bacterial Symbionts use a type VI secretion system to eliminate competitors in their natural host
Abstract: Most host-associated microbial communities are composed of diverse bacterial populations that perform critical services for their symbiotic partners including nutrient cycling, protection from predators, and defense against disease. Recent work suggests co-occurring populations of symbiotic bacteria participate in complex social interactions such as competition for an ecological niche within the host. The vibrio-squid symbiosis is an excellent model system for studying interbacterial interactions because multiple strains of Vibrio fischeri are found co-inhabiting the light organs of adult Euprymna scolopes squid. To understand how these microbial populations interact and possibly compete for light organ colonization, we performed culture-based co-incubation assays in which two strains were mixed in a ~1:1 ratio and incubated for 5-24 hours after which the abundance of each strain was measured. We found V. fischeri isolates display two behavior types: lethal and non-lethal, where lethal strains eliminate non-lethal strains through a contact-dependent mechanism, and non-lethal strains coexist without conflict. To identify the genetic determinants of inter-strain killing, we performed comparative genomics of two strains MJ11 (lethal) and ES114 (non-lethal), and found that MJ11 encodes a type VI secretion system on chromosome II (T6SS2) that is absent in ES114. Disruption of an essential structural component of T6SS2 inhibited the killing phenotype, allowing non-lethal and lethal strains to coexist. To determine if T6SS2-mediated killing influences crypt colonization frequency, we used a two-strain colonization assay with a non-lethal strain and either the wildtype lethal strain, or the T6SS2 mutant. Co-infection of wildtype strains resulted in crypt incompatibility; the lethal and non-lethal strains were never observed co-colonizing the same crypt. However, co-infection of the non-lethal strain with the T6SS2 mutant resulted in co-colonized crypts up to 40% of the time. These findings indicate that V. fischeri use T6SS2 to compete for host colonization sites and co-habitation of non-lethal and lethal strains in a single light organ requires a disruption of T6SS2 function or physical separation of strains in different crypts.