FEMS Microbiology Ecology 13 (1994) 177-184 © 1994 Federation of European Microbiological Societies 0168-6496/94/$07.00 Published by Elsevier 177 FEMSEC 00496 Effects of enhanced UV-B irradiation on the red coloured freshwater flagellate Euglena sanguinea Sabine Gerber and Donat-P. H~ider * Institut fiir Botanik und Pharmazeutische Biologie, Friedrich-Alexander-Universitiit, Staudtstr. 5, D-91058 Erlangen, FRG (Received 29 April 1993; revision received 29 September 1993; accepted 30 September 1993) Abstract: Euglena sanguinea, a freshwater flagellate isolated from a pond in the Ffiinkische Schweiz, orients itself in its habitat exclusivelyby positive phototaxis, which leads the organisms to the surface where they form a neuston. The algae are coloured red, as they contain haematochrome, a mixture of carotenoids, the main component being astaxanthin diester. Absorption spectroscopy shows that astaxanthin diester accumulates in cells irradiated with artificial UV-B irradiation, which suggests that the carotenoid is a photoprotective pigment. 15% enhanced UV-B irradiation impairs photoorientation and motility and photobleaches chlorophyll a while the carotenoids are less affected. Key words: Euglena sanguinea; Flagellate; Haematochrome; Phototaxis; Ultraviolet radiation Introduction Recent investigations have shown that many phytoplankton organisms are quite sensitive to- wards UV-B radiation [1]. Even at ambient levels of UV-B radiation a number of organisms seem to be under UV stress, depending on the time of the year and the geographical position. Smith et al. [2] have shown that increased UV-B irradia- tion during the austral spring ozone hole (a thin- ning of the stratospheric ozone by 50% in 1990) has reduced the primary production of phyto- plankton in the marginal ice zone by 6-12%. Phytoplankton organisms dwell in the upper layers of the water column, the photic zone, as they depend on sunlight for photosynthesis [3]. * Corresponding author. Tel: (09131) 858216; Fax: (09131) 858215. Many motile phytoplankton algae orient them- selves in their habitat guided by external stimuli such as light, chemical gradients or gravity to find places of suitable conditions for their growth [4], which on the one hand allow photosynthesis, but on the other hand do not harm the cells. UV-B radiation has been found to impair motility and orientation in Euglena gracilis, a species closely related to E. sanguinea: even short exposure to artificial UV-B irradiation or to solar radiation decreased the percentage of motile cells and reduced the swimming velocity of the organ- isms. The use of cut-off filters or an artificial layer of ozone which removes the shorter wave- length radiation resulted in less inhibition, indi- cating that the UV-B component of the solar radiation is most detrimental [5]. Photosynthesis is impaired by artificially en- hanced UV-B radiation [6-8]. Investigations on SSDI 0168-6496(93)E0056-N Downloaded from https://academic.oup.com/femsec/article-abstract/13/3/177/655860 by guest on 22 May 2020