Effects of enhanced UV-B irradiation on the red coloured freshwater flagellate Euglena sanguinea

Euglena sanguinea, a freshwater flagellate isolated from a pond in the Frankische Schweiz, orients itself in its habitat exclusively by 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.