Description:
An epifluorescence microscopy method using the fluorescent dye acriflavine is described for direct detection and enumeration of the fungilike 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 yellow-green. Photosynthetic protists were distinguished by autofluorescence of pigments and protozoans by absence of cell-wall fluorescence. Several natural phytoplankton samples from the North Sea were examined with this technique, where up to 5.4 × 106cells of thraustochytrids were found per gram dry weight of sample. The results suggest that thraustochytrids might be much more abundant in natural samples that previously suspected.