DNA Degradation in Wild-type and Repair-deficient Strains of Salmonella typhimurium Exposed to Ultraviolet Light or Photodynamic Treatment

Abstract

Five mutants of S. typhimurium strain LT2 trpD1 (Cole1)+, initially detected because they released little or no colicin when tested on solid medium, were sensitive to UV light. Further testing indicated that 1 of the mutants was deficient in genetic recombination and was probably a recA-type mutant, while 3 of the others were deficient in DNA polymerase activity and appeared to be typical polA mutants. The 5th mutant was less sensitive than the others to methyl methanesulfonate, showed reduced proficiency in genetic recombination, and was of approximately normal UV mutability. This mutant may be a counterpart of the class known as urvD in Escherichia coli. All 5 mutants degraded significantly more of their DNA following exposure to UV than did the wild-type strain. The recA-type mutant and the possible uvrD mutant also degraded significantly more of their DNA spontaneously than did the wild-type. Treatment with visible light and acridine orange (photodynamic treatment) caused no significant degradation of DNA in the wild-type strain, a highly significant increase in the extent of DNA degradation in a polA mutant, and a decrease in the extent of degradation in the recA-type mutant.