B38: Characterizing DarHTG3, a toxin-antitoxin system in Escherichia coli

Presenter(s)

Nico Carlson

Abstract or Description

Phage therapy is a possible alternative to antibiotics which could selectively target multi-drug-resistant bacterial infections. Studying bacterial phage defense helps us understand the arms race between phage and bacteria and apply it to phage therapies. DarTG1 and DarTG2, two toxin-antitoxin phage defense systems found in Escherichia coli, are characterized by toxins that ADP-ribosylate DNA and antitoxins that reverse this modification. DarHTG3, a predicted third DarTG system, was recently found through a bioinformatic analysis. It contains a toxin with homology to darT1 and darT2 encoded adjacent to a predicted ADP-ribosyl glycohydrolase (ARG) as well as a third gene predicted to be a helicase. We hypothesize that this three-gene cluster is a third type of toxin-antitoxin phage defense system in which darT3 is the toxin, darG3 is the antitoxin, and the predicted helicase is somehow required for sensing phage infection. Plaque assays determined that DarHTG3 defends against a different and broader range of phages compared to DarTG1 and DarTG2. Strains with deletions of the helicase and toxin compared to DarHTG3 and a control strain were performed but were inconclusive due to phenotypic variability linked to the native promoter. The next steps will be to clone a version of DarHTG3 on an inducible promoter without the helicase or toxin to study their roles in phage defense. The specificity of the toxin and antitoxin will be tested by combining them with the antitoxins from DarTG1 and 2 to determine if these antitoxins can counteract DarHTG3’s toxicity.