MICROSPECTROFLUOROMETRY, FLUORESCENCE IMAGING AND CONFOCAL MICROSCOPYOF AN ENDOGENOUS PIGMENT OF THE MARINE CILIATE FABREA-SALINA

Fabrea salina, an apparently colorless marine ciliate in the order Het erotrichicia, shows positive phototaxis and photophobic step-down reac tions. Fluorescence microscopy and imaging of living cells reveal only a scarcely detectable emission, but dead cells are characterized by a strong red fluorescence, results indicating the presence of an endoge nous fluorescent pigment. Single cell microspectrofluorometry, fluores cence imaging and laser confocal microscopy studies, together with tim e-gated fluorescence spectroscopy of cell suspensions, were performed in order to investigate the nature and localization of this pigment. T he fluorescence emission spectrum dr different excitation wavelengths (from 337 to 425 nm) exhibits two peaks: the main one between 590 and about 615 nm, depending on the cell treatment, and the other one at ab out 655 nm. The time decay of fluorescence shows three distinct compon ents, with lifetimes ranging from a few hundred picoseconds to some na noseconds and relative contributions varying with the chemical treatme nt. Time-gated spectroscopy allows us also to observe differences in t he spectral features of the distinct emitting species. Laser confocal microscopy reveals that the pigment is localized just below the cell m embrane. The spectral and temporal fluorescence features of the endoge nous pigment present in F. salina are very similar to the ones of blep harismin, the pigment of Blepharisma japonicum, thus suggesting that t he F. salina pigment might aslo be a hypericin-like pigment.