Relative effectiveness of the 300–320 nm spectral region of sunlight for the production of primary lethal damage in E. coli cells

Abstract

Cell inactivation by sunlight exposure has been studied in E. coli CSR 603 ( uvrA recA phr), a K12 derivative which is deficient in all known repair systems. Under suitable conditions, unfiltered sunlight inactivates these cells to 10 −3 survival within 30 sec. The effects of unfiltered sunlight have been compared with those of sunlight filtered through 1-cm layers of aqueous caffeine solutions ranging in concentration from 1 to 20 mg/ml. In the wavelength region of solar emission below 320 nm, which is most critical for DNA damage, the transmission of these liquid filters changes from 10 to 90% within 8-nm intervals. Thus our results permit minimum estimates for the fraction of lethal lesions produced by the solar spectrum below certain wavelengths. In an experiment analyzed in this manner more than 80% of primary lethal lesions are caused by wavelengths <312 nm, and more than 50% by wavelengths <306 nm, while the contribution of wavelengths >380 nm to primary lethal damage is below 1%.