Effects of UV-B irradiation on the motility and photo motility of the marine ciliate Fabrea salina

Fabrea salina is a motile ciliate marine protozoan that belongs to the order Heterotrichida, and which exhibits photomotile reactions. We report here the results of a study on motility and phototaxis of F. salina exposed to artificial UV irradiation. The UV-A radiation component does not induce any alteration in the motile or photomotile behavior; UV-B radiation causes a significant increase in cell speed, even after short exposure times, and totally inhibits the phototactic reaction after 60 min of irradiation. The speed increase is transient, whereas the phototactic reaction is irreversibly damaged. Fluorescence measurements indicate that there is no apparent damage to one of the potential candidates for photoreception in F. salina, i.e. a hypericin-like pigment. Phototactic sensitivity curves show that a higher fluence rate is required to obtain a half-maximum response in UV-B-treated samples compared with the rate required for the controls, while the saturation level of the phototactic response is definitely lower in UV-irradiated samples. These results suggest that UV-B irradiation may damage cell structures, such as membrane channels, and may also alter important functions, such as photosensory transduction.