Direct effects of UV-B radiation on the freshwater heterotrophic nanoflagellate Paraphysomonas sp.
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 degrees 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 degrees C suffered 100% mortality except at the lowest UV-B level (with PRR) tested, which suggested a photorepair temperature optimum above 15 degrees 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.
Department of Biology, Temple University, Philadelphia, PA 19122, USA.
Amy L
AL
Macaluso
David L
DL
Mitchell
Robert W
RW
Sanders
D000818:Animals; D002470:Cell Survival; D044523:Chrysophyta / Q000502:physiology / Q000528:radiation effects*; D004249:DNA Damage; D004260:DNA Repair; D016054:DNA, Protozoan / Q000737:chemistry / Q000235:genetics; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D056890:Eukaryota / Q000502:physiology / Q000528:radiation effects*; D005618:Fresh Water / Q000469:parasitology*; D020459:Genes, rRNA; D008969:Molecular Sequence Data; D016053:RNA, Protozoan / Q000235:genetics; D012337:RNA, Ribosomal, 18S / Q000235:genetics; D017422:Sequence Analysis, DNA; D014466:Ultraviolet Rays
D016054:DNA, Protozoan; D004275:DNA, Ribosomal; D016053:RNA, Protozoan; D012337:RNA, Ribosomal, 18S