AN EPIFLUORESCENCE MICROSCOPY METHOD FOR DIRECT DETECTION AND ENUMERATION OF THE FUNGI-LIKE MARINE PROTISTS, THE THRAUSTOCHYTRIDS

An epifluorescence microscopy method using the fluorescent dye acrifla vine is described for direct detection and enumeration of the fungilik e protists, the thraustochytrids, in natural samples. The technique is based on the principles that the fluorochrome stains thraustochytrid cell walls containing sulfated polysaccharides red and the nucleus yel low-green. Photosynthetic protists were distinguished by autofluoresce nce of pigments and protozoans by absence of cell-wall fluorescence. S everal natural phytoplankton samples from the North Sea were examined with this technique, where up to 5.4 x 10(6) cells of thraustochytrids were found per gram dry weight of sample. The results suggest that th raustochytrids might be much more abundant in natural samples than pre viously suspected.