UV mutagenesis in Escherichia coli K-12: Cell survival and mutation frequency of the chromosomal genes lacZ, rpoB, ompF, and ampA

UV-induced mutation frequency and cell survivability was examined in Escherichia coli K12 strains. The effects of UV (254nm) induced damage on deoxyribonucleic acid (DNA) was investigated using two protocols termed Direct-Plate Irradiation (DPI) and Liquid-Plate Irradiation (LPI). A biological system needed to be designed to facilitate future experiments involving UV and gene mutation frequencies. The conditions for the DPI protocol involved plating E. coli onto nutrient agar plates and exposing them to 0, 5, 10, and 15 seconds of UV irradiation at 60cm away from the plates. The LPI protocol involved exposing cells suspended in M9-minimal salts with 0.2% MgSO4 to 0, 10, 20, 30, 40 and 60 seconds. Both negative screening and positive screening procedures were applied to determine the mutational frequency of lacZ, rpoB, ompF, and ampC. Several strains and plasmids were also tested in these selections to determine the best biological system for carrying out the experiment. These tests showed that the best strain was B23. This strain produced a maximum mutational frequency of 8.5 x 10 for rpoB (rifampicin resistance) and 1.5 x 10 for ompF (chloramphenicol resistance). The results are discussed in terms of the SOS response or SOS system because this system is responsible for mutagenesis. Our results provide a framework for future assays involving mutagenesis.