FIGURE 3.

Resistance to DNA damaging agents in the Thermus thermophilus mutants. (A) The HB27pyrEK control strain and the ppol:kat and addAB:kat insertion mutants were subjected to different DNA damaging agents. The cell cultures were incubated at 65°C until OD₆₀₀ of 0.3 (3 × 10⁸ cell/ml) was reached. Then, cells were further incubated for 2 h with the indicated concentrations of the different DNA damaging agents: peroxide hydrogen (H₂O₂), 4-Nitroquinoline-N-oxide (4-NQO) and Bleomycin (Bleo). Then, 10 μl of serial decimal dilutions were drop-inoculated on non-selective plates that were incubated at 65°C for 48 h. Fraction of surviving cells following DNA damage (4-NQO, left. Bleo, medium. H₂O₂, right) is calculated relative to an untreated control. (B) The HB27 control strain and its derivatives ppol:lox72, ppol_cat, ppol_comp, addAB:lox72, and addAB_ppol mutants were subjected to the same DNA damaging agents used in panel (A). Each data point is an average of at least five biological replicates. Error bars correspond to the standard deviation of the means.