Comparative mutagenesis of Escherichia coli strains with different repair deficiencies irradiated with 222-nm and 254-nm ultraviolet light
Photoinactivation and reversion to tryptophan prototrophy were studied in four Escherichia coli strains with different repair deficiencies. Cells were irradiated with 222-nm wavelength UV emitted by an excimer lamp and with 254-nm wavelength UV emitted by a low-pressure mercury lamp. Strain DSM 9494 (trp− uvrA+) turned out to be most resistant while the strain DSM 9495 (trp− uvrA-), which is defective in nucleotide-excision repair (NER)wasmost sensitive to bothwavelengths. UV-fluence rates for a respective inactivation were twice as high for 222-nm wavelength UV than for 254-nm UV. No clear difference in efficiency of inactivation could be observed between the two wavelengths in strains DSM 9496 (trp− uvrA+ pKM101) and DSM 9497 (trp− uvrA− pKM101). In general,more revertantswere induced by 254-nmwavelength UV, whichcorroborates thehypothesis that a higher amount of DNA damage was induced by this wavelength than by 222-nm UV, except for DSM 9497 where no clear difference could be observed regarding the number of revertants induced by both wavelengths. This strain DSM 9497 has a high sensitivity to certain oxidative mutagens compared with other strains, which is indicative of formation of reactive oxygen species during irradiation with 222-nm wavelength UV.
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