ABSTRACT
Vibrio cholerae is a Gram-negative bacterium that inhabits marine ecosystems but causes life-threatening cholera disease when ingested by humans. Like approximately 25% of all Gram-negative bacteria, V. cholerae uses the Type VI Secretion System (T6SS) to deliver cytotoxic proteins in a contact-dependent manner to eliminate adjacent cells. After sequencing a diverse set of V. cholerae isolates, we discovered two putative T6SS toxins, which I named TleV1 and TpeV. TleV1 is lethal when expressed in the periplasm of Escherichia coli cells and can be delivered in a T6SS-dependent manner to compromise cell membranes and kill target bacteria. Unlike other V. cholerae T6SS effectors, TpeV does not share homology to proteins with known functions. E. coli cells expressing periplasmic TpeV exhibit profound toxicity, have a disrupted membrane potential and are permeabilized. I determined that V. cholerae can translocate TpeV to permeabilize and kill target cells in a T6SS-dependent manner. Important human, animal and plant pathogens encode tpeV homologs adjacent to known T6SS genes, indicating that the toxin belongs to a large protein family. While many studies have described the regulation and toxins of the T6SS, few have investigated the defensive responses elicited by cells that are targeted by T6SS attacks. I demonstrated that multiple human commensal E. coli strains, which are highly susceptible to killing via the T6SS, show a remarkable survival improvement when co-cultured with V. cholerae in the presence of glucose. I identified that the E. coli glucose-responsive master gene regulator CRP (cyclic AMP receptor protein) controls resistance against T6SS attacks. E. coli cells with a crp gene disruption are protected against V. cholerae T6SS attacks even in the absence of glucose. In summary, I found that V. cholerae isolates employ diverse chemical weapons to eliminate competitor cells and identified a small molecule that confers protection against T6SS attacks in target cells.


The F. L. (Bud) Suddath Memorial Award has been established by the family, friends and colleagues of Bud Suddath to stimulate graduate research in the fields of biology, biochemistry and biomedical engineering. The award is given annually to current Georgia Tech Ph.D. candidates in any field of study who are conducting biological or biochemical research at the molecular or cellular level. The awardee is provided an award of up to $1,000 in value which may be used to facilitate the completion of his or her scholarly development, and they will be invited to present their work at a special event hosted by the Petit Institute at the start of the upcoming annual Suddath Symposium. The recipient of this award will also have his or her name engraved on a commemorative plaque in the Suddath Seminar Room in the Petit Biotech building at Georgia Tech.