Regulation of the type VI secretion system controls lethal interactions in the squid symbiont Vibrio fischeri ES401 (2016)

Undergraduate: Stephanie Smith

Faculty Advisor: Alecia Septer
Department: Biology

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Vibrio fischeri is a bioluminescent marine bacterium that associates with the Hawaiian Bobtail Squid, Euprymna scolopes. This symbiosis is considered a model system for studying bacterial-animal interactions, quorum sensing, and bioluminescence. The genome of V. fischeri strain ES401 encodes a type VI secretion system (T6SS) that gives it the ability to kill other V. fischeri strains, presumably by injecting toxic proteins into competing cells. Although this T6SS is broadly distributed among host-associated marine bacteria, not all V. fischeri strains have this unique ability to kill. The goal of this research project was to determine the regulatory pathways that control expression of the genes responsible for this lethal behavior. Transposon mutagenesis was performed on an ES401 reporter strain designed to turn blue when the T6SS is being expressed. This reporter strain was subjected to random transposon mutagenesis and approximately 15,000 mutants were screened for white colonies, indicating the T6SS regulatory pathway was disrupted and the lethal behavior might be switched off. Arbitrary PCR was used to map the individual transposon insertion sites within these mutants. Preliminary sequencing results of the PCR products revealed that two of the three transposon insertions mapped within the T6SS gene cluster, suggesting that the T6SS may be self-regulating. These findings suggest that multiple genes are likely involved in the regulation of the T6SS, and its lethal behavior.