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McNair Scholars Program

Theresa Barke, Ph.D.

she/her

Education: Bachelor of Science in biology (August 2011)

Doctor of Philosophy in pathology, microbiology, and immunology at Vanderbilt University

McNair Project: The Role of Lgt and LspA in Lipoprotein Modification and  its Impact on the Heme Regulation in Enterococcus faecalis (2011)

Mentor: Lynn Hancock, Ph.D.

Lipid modified peripheral membrane proteins undergo a series of enzymatic modifications in their journey from pre-prolipoproteins to mature lipoproteins. Acylation of hydrophilic proteins by the enzyme, lipoprotein diacylglyceryl transferase (Lgt), facilitates its embedding within the hydrophobic lipid membrane. Lipoprotein signal peptidase (Lsp) is responsible for cleaving the signal sequence from the embedded prolipoprotein resulting in a mature lipoprotein. The cleaved signal sequence undergoes further processing by other proteases resulting in small linear peptides known as sex pheromones which are excreted by plasmid-free strains of E. faecalis and facilitate plasmid transfer with conjugative plasmid carrying donor strains. It was hypothesized that the deletion of lgt and lsp would affect the downstream processing and production of sex pheromones leading to a decrease in transconjugation efficiency between donor and recipient strains. Lgt and lsp isogenic mutants were created in E. faecalis FA2-2 using markerless gene deletion techniques. Transconjugation efficiency was determined using the isogenic lgt and lsp mutants as recipient strains and three OG1SSp strains carrying the plasmids, pCF10, pAM714, and pAM378, as donor cells. Successful conjugal transfer of plasmids was determined by the acquisition of antibiotic resistance as a marker. It was determined that while the deletion of lgt in the recipient FA2-2 strain showed little impact on the ability of E. faecalis to successfully transfer plasmids, the deletion of lsp resulted in a significantly decreased number of plasmid transfer events.