AME 40:283-292 (2005)  -  doi:10.3354/ame040283

Photoreactivation in two freshwater ciliates: differential responses to variations in UV-B flux and temperature

Robert W. Sanders1,*, Amy L. Macaluso1, Thomas J. Sardina1, David L. Mitchell2

1Biology Department, Temple University, Philadelphia, Pennsylvania 19122, USA
2University of Texas M.D. Anderson Cancer Center, Science Park/Research Division, Smithville, Texas 78957, USA

ABSTRACT: The effects of UV-B radiation on 2 ciliate species (Glaucoma sp. and Cyclidium sp.) from a clear oligotrophic lake were examined under laboratory conditions with and without photoreactivating radiation (PRR: UV-A and visible light). Glaucoma sp. was exposed to 3 UV-B intensities at 4 temperatures to simulate a range of environmentally relevant conditions. Population growth of Glaucoma sp. declined with increasing levels of UV-B exposure in treatments receiving PRR; blocking PRR generally resulted in 100% mortality. Occurrence of cyclobutane pyrimidine dimers (CPDs [mb DNA]–1) was significantly reduced in Glaucoma sp. receiving PRR relative to those without PRR. These data indicate that photoenzymatic repair is a major component of UV-B tolerance in Glaucoma. At UV-B levels that Glaucoma sp. tolerated, Cyclidium sp. suffered 100% mortality and accumulated a similar level of CPDs whether or not PRR was blocked. Incubation of the 2 ciliates under UV-transparent and UV-blocking acrylics in the oligotrophic lake confirmed their relative sensitivities to UV radiation (UVR). Photoenzymatic repair in Glaucoma sp. was more efficient at 20°C than at 10, 15 and 25°C. The temperature-dependent nature of photoenzymatic repair underscores the need to consider the interactive effects of temperature and UVR on biota, particularly in the face of global climate change and rising incident UVR due to ozone depletion.

KEY WORDS: Ultraviolet radiation · UV-B · Photoreactivation · Photoenzymatic repair · Ciliates · Cyclobutane pyrimidine dimers · Temperature · Glaucoma · Cyclidium

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