UV-light survival and mutagenesis in P . putida KT2440 and its Δ ppk and Δ ppx mutant derivatives. (A) UV sensitivity tests were performed in P. putida KT2440 (wt) and its Δppk and Δppx mutant derivatives streaked out onto LB plates by means of a gradient of UV irradiation (with exposure time ranging from 0 to 100 s). Irradiations were performed at 254 nm (400 μW/cm2), and the boundaries of different irradiation periods of time are indicated by vertical dashed lines. (B) Frequency of spontaneous Rif-resistant mutants in stationary-phase cells of P. putida KT2440 (wt) and its Δppk and Δppx mutant derivatives grown on M9 minimal medium with either 0.2% (w/v) glucose or succinate. Frequencies were calculated by dividing the average number of Rif-resistant colonies by the total number of viable cells in the same culture. Bars represent the mean value of the frequency of Rif-resistant clones ± SD of duplicate measurements from at least two independent experiments.