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 photosynthetically active radiation) as well as the effect of simulated sunlight upon the physiological state of Escherichia coli in fresh water were evaluated. Simulated solar radiation had a sublethal effect on E. coli populations in a short-lime exposure by provoking loss of culturability and the formation of viable but nonculturable cells. Prolonged exposure increased the damage to cells but cellular integrity was never affected. However, important differences between the way the sunlight components acted were detected. After photosynthetically active radiation (PAR) exposure, cells remained metabolically 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 after 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 that of simulated sunlight exposed cells. The effect of simulated solar radiation 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.