Differentiation and Characterization of Individual Phototrophic and Heterotrophic Microflagellates by Sequential Epifluorescence and Electron Microscopy

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Abstract
Epifluorescence microscopy was used to discriminate between phototrophic and heterotrophic nanoplankton from natural plankton samples prior to examination by EM. In this procedure, sea-water samples are dried onto Formvar-coated transmission electron microscopy grids and examined with epifluorescence microscopy to denote the location of all photosynthetic microorganisms, visible because of chlorophyll fluorescence. Both the photosynthetic and non-photosynthetic cells can then be located by transmission and scanning electron microscopy after shadow-casting or coating with AuPd for critical examination of taxonomic features. This technique allows the detailed characterization of, and discrimination between, numerically dominant phototrophic and heterotrophic nanoplankton species in natural plankton populations, including cells that evade study by culture methods.