Date of Award

Spring 5-9-2020

Document Type

Honors Thesis



First Advisor

Keith Weaver

Second Advisor

Michael Chaussee

Third Advisor

Bernie Wone


toxin-antitoxin systems, E. faecalis, plasmid pAD1, parEF0409, bacterial toxins, expression vector

Subject Categories

Bacteria | Bacteriology | Biology | Medical Cell Biology | Medical Microbiology | Organismal Biological Physiology


Toxin-antitoxin (TA) systems were originally identified as two-component systems ensuring the stable inheritance of plasmids in bacterial populations. Recently, they have been identified on bacterial chromosomes where their functions remain mostly undefined. The par locus of E. faecalis plasmid pAD1 (parpAD1) was the first TA system defined in a Gram-positive bacterium and a homolog encoded on the E. faecalis chromosome (parEF0409) was later described. Related loci numbering in the hundreds have been identified throughout Gram-positive bacteria based on homology to the toxin of the system, Fst, and similarities in genetic organization and regulation. Despite their similar sequences, over-expression of FstpAD1 and FstEF0409 have differing effects on the host transcriptome, suggesting that sequence differences between the toxins are fine-tuned for distinct functions. Using a combination of domain swaps, as well as single and double amino acid changes, we identified key amino acid residues between FstEF0409 and FstpAD1 critical for triggering an FstpAD1-like response. This finding helps define the critical region of toxin specificity and will aid in determining the mechanism of action of this large family of peptide toxins.



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