Date of Award

8-2015

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Biological Sciences

Advisor

Cao, Min

Committee Member

Hughes, Thomas

Committee Member

Dong, Yuqing

Abstract

Vibrio cholerae is a Gram-negative, rod-shaped bacterium that is mainly found in water environments, and is the causative agent of the disease cholera in humans. It is critical for this bacterium to communicate via quorum sensing to persist and survive in the environment, as well as cause infection. Recently, it has been shown that eukaryotes are able to sense and respond to certain quorum sensing molecules, known as autoinducers, which are produced by different bacteria. Caenorhabditis elegans is a particularly useful model for studying this interaction. During preliminary experiments, it was noticed that C. elegans were strongly attracted to V. cholerae C6706 O1 El Tor, although this bacterium kills the nematodes at a high rate and significantly decreases lifespan. To further study this phenomenon, chemotaxis assays and lifespan assays were conducted using C. elegans N2 strain. Different Vibrio spp. were tested (V. cholerae, V. harveyi, and V. fischeri) to figure out what underlying molecules were driving chemoattraction behavior in C. elegans. It was found that C. elegans can sense various autoinducer molecules with preferences, but other signaling molecules also appear to be involved in chemotaxis behavior. Interestingly, the ability of V. cholerae to attract C. elegans N2 seems to be dependent on ToxT, which activates the transcription of virulence genes that are necessary for pathogenesis and leads to increased levels of cyclic GMP-AMP (c-GAMP), a recently identified new second messenger that has only been reported in V. cholerae. It is thus hypothesized that cyclic di-nucleotides, specifically c-GAMP and c-di-GMP, are playing an important role influencing host behavioral modifications. It has been shown that 1nM concentrations of both c-GAMP and c-di-GMP are able to influence a positive chemotactic response in C. elegans. Through lifespan assays, killing of C. elegans by V. cholerae also appears to be dependent on ToxT, but not DncV, which is the cyclase responsible for the production of c-GAMP. This work will ultimately allow for a better understanding of the specific mechanisms involved in interkingdom communication, as well as shed light on how V. cholerae O1 El Tor is able to persist and cause disease within a host.

Included in

Biology Commons

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