A study exposed 3 unknown bacterial strains (A, B, C) and a wildtype strain to DNA damaging agents UV, H2O2, and NaNO2 to determine which DNA repair pathways were mutated. UV causes thymidine dimers repaired by nucleotide excision repair, H2O2 causes guanine oxidation repaired by base excision repair, and NaNO2 causes cytosine deamination repaired by base excision repair. The survival rates will indicate which pathways are mutated in each unknown strain.