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Applied and Environmental Microbiology, July 2009, p. 4525-4530, Vol. 75, No. 13
0099-2240/09/$08.00+0     doi:10.1128/AEM.02803-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Direct Effects of UV-B Radiation on the Freshwater Heterotrophic Nanoflagellate Paraphysomonas sp.{triangledown}

Amy L. Macaluso,1 David L. Mitchell,2 and Robert W. Sanders1*

Department of Biology, Temple University, 1900 North 12th Street, Philadelphia, Pennsylvania 19122,1 University of Texas M. D. Anderson Cancer Center, Science Park/Research Division, Smithville, Texas 789572

Received 10 December 2008/ Accepted 30 April 2009

The formation of DNA photoproducts in organisms exposed to ambient levels of UV-B radiation can lead to death and/or reduced population growth in aquatic systems. Dependence on photoenzymatic repair to reverse DNA damage caused by UV-B radiation is demonstrated for Paraphysomonas sp., a member of a widely distributed genus of heterotrophic nanoflagellates. At 20°C, Paraphysomonas sp. was exposed to a range of UV-B intensities encountered in natural systems. Populations of the flagellate survived and grew in a dose-dependent manner, but only when simultaneously exposed to photorepair radiation (PRR). In contrast, flagellates exposed to UV-B at 15°C suffered 100% mortality except at the lowest UV-B level (with PRR) tested, which suggested a photorepair temperature optimum above 15°C. After acute UV-B exposures, DNA damage (measured as the formation of pyrimidine dimers) was reduced only in organisms that underwent subsequent exposure to PRR. Populations kept in the dark after UV-B exposure maintained the initial levels of pyrimidine dimers. These results are the first to demonstrate the reliance of a heterotrophic flagellate on photoenzymatic DNA repair for survival from UV-B exposure.

* Corresponding author. Mailing address: Department of Biology, Temple University, 1900 North 12th St., Philadelphia, PA 19122. Phone: (215) 204-2056. Fax: (215) 204-6646. E-mail: robert.sanders{at}temple.edu

{triangledown} Published ahead of print on 8 May 2009.

Applied and Environmental Microbiology, July 2009, p. 4525-4530, Vol. 75, No. 13
0099-2240/09/$08.00+0     doi:10.1128/AEM.02803-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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