Protozoa and UV Radiation
prepared by Bob Sanders
The degree to which natural levels of UV exposure are deleterious to protists is species-specific and varies substantially - even between closely related species. The freshwater heterotrophic flagellate, Bodo saltans, and two marine flagellates, Paraphysomonas bandaiensis and P. imperforata, had reduced motility and feeding when exposed to UV-A radiation (Ochs 1997; Sommaruga et al. 1996). B. saltans and B. caudatus also accumulated greater DNA damage after exposure to UV-B than did chrysomonad or cryptomonad flagellates (Sommaruga and Buma 2000). The ciliate Stentor coerulus was sensitive to UV-B exposure (Häder and Häder 1991), but S. araucanus showed no difference in the proportion of survivors when treatments were shielded from UVR (Modenutti et al. 1998). During in situ incubations of arctic ciliate populations, UV-B had strong negative effects on Askinasia sp. and Bursaridium sp., moderate negative effects on Halteria sp. and Strombidium sp., and no apparent effect on Urotricha sp. (Wickham and Carstens 1998). Our research on the protozoa isolated from the UV-transparent Lake Giles - ciliates Cyclidium sp. and Glaucoma sp., and the heterotrophic flagellate Paraphysomonas vestita - also indicate a wide range of sensitivities to UV-B exposure (Sanders, et al., submitted; Sanders and O'Brien 2002).
Below are examples of Cyclidium, Glaucoma, and Strombidium (l to r)
The variation in UV susceptibility of protistan species to UV radiation likely reflects differences in both physiology and behavior. Protists are capable of vertical migration, and the attenuation of UV radiation would reduce its negative effects in species that migrate to, or remain in, deeper water during the day. In addition, the ability to repair UV-induced damage to DNA should be as widespread in protozoa as it is in other organisms. Photoenzymatic repair (PER) - one major mechanism for mending DNA damage caused by UV-B radiation - has been demonstrated for the ciliate Paramecium tetraurelia and some photosynthetic dinoflagellates (Litchman et al. in press; Smith-Sonneborn 1979). Sanders and colleagues found strong dependence on photoenzmatic repair in Glaucoma sp. and P. vestita exposed to UV-B radiation, but no evidence of PER for the species of Cyclidium isolated from the same lake (Giles). Taken together, these data indicate a surprising degree of heterogeneity in protists' tolerance to UV radiation - even within the same environment.
Häder, D. P., and M. A. Häder. 1991. Effects of solar radiation on motility in Stentor coeruleus. Photochemistry and Photobiology 54:423-428.
Litchman, E., P. J. Neale, and A. T. Banaszak. 2002. Increased sensitivity to ultraviolet radiation in nitrogen-limited dinoflagellates: photoprotection and repair. Limnology and Oceanography 47:86-94.
Modenutti, B. E., E. G. Balseiro, and R. Moeller. 1998. Vertical distribution and resistance to ultraviolet radiation of a planktonic ciliate, Stentor araucanus. Internationale Vereingung für Theoretische und Angewandte Limnologie, Verhandlungen 26:1636-1640.
Ochs, C. A. 1997. Effects of UV radiation on grazing by two marine heterotrophic nanoflagellates on autotrophic picoplankton. Journal of Plankton Research 19:1517-1536.
Sanders, R.W., T.J. Sardina, and A.L. O'Brien. Submitted. Photoreactivation in freshwater ciliates: responses to variations in UV-B flux and temperature.
Sanders, R.W. and A.L. O'Brien. A major role for photoenzymatic repair (PER) in a freshwater heterotrophic flagellate exposed to UV-B radiation. Abstracts, American Society of Limnology and Oceanography, Victoria, BC, Canada. June 2002.
Smith-Sonneborn, J. 1979. DNA repair and longevity assurance in Paramecium teteurelia. Science 203:1115-1117.
Sommaruga, R., Oberleiter, and R. Psenner. 1996. Effect of UV radiation on the bacterivory of a heterotrophic nanoflagellate. Applied and Environmental Microbiology 62:4395-4400.
Sommaruga, R., and A. G. J. Buma. 2000. UV-induced cell damage is species-specific among aquatic phagotrophic protists. Journal of Eukarotic Microbiology 47:450-455.
Wickham, S. and M. Carstens. 1998. Effects of ultraviolet-B radiation on
two arctic microbial food webs. Aquatic Microbial Ecology 16:163-1
last modified on Feb 12, 2009