The effect of simulated solar radiation on Escherichia coli: The relative roles of UV-B, UV-A, and photosynthetically active radiation

The relative role of components of solar radiation (UV-B, UV-A, and photosy nthetically active radiation) as well as the effect of simulated sunlight u pon the physiological state of Escherichia coli in fresh water were evaluat ed. Simulated solar radiation had a sublethal effect on E. coli populations in a short-lime exposure by provoking loss of culturability and the format ion of viable but nonculturable cells. Prolonged exposure increased the dam age to cells but cellular integrity was never affected. However, important differences between the way the sunlight components acted were detected. Af ter photosynthetically active radiation (PAR) exposure, cells remained meta bolically active but only 10% of the cells were culturable. When cells were exposed to UV-A, the culturable fraction was similar to the one obtained a fter PAR irradiation, although formation of viable but nonculturable cells was not observed. For UV-B radiation short-time exposures (6 h) were enough to provoke loss of culturability and a reduction in activity similar to th at of simulated sunlight exposed cells. The effect of simulated solar radia tion on E. coli cells was mainly attributable to shorter wavelengths, but a synergistic interaction of the UV-B, UV-A and PAR components was detected.