Improved filtration techniques for the concentration and cytological preservation of microalgae for electron microscopy

Abstract

A gentle filtration technique is described for concentration and fixation of phytoplankters directly on Millipore membranes, followed by subsequent removal of the membrane and embedment of the cellular material in epoxy resin. The technique shows excellent preservation of cell morphology, especially of fragile algal cells (dinoflagellates, zoospores, etc.), with little loss of material, and affords permanently fixed samples for both light and electron microscopy. It is ideally suitable for handling small amounts of algal cultures and for frequent sampling of such cultures in time-sequence studies. Adaptations of the technique are described which enable (1) high proportion of flagella preservation, (2) successful concentration of algal cells from water samples of low population density, and (3) convenient preparation of samples for "freeze-etching" or histochemical studies. A further application to scanning electron microscopy is described, where the replacement of Millipore membranes by Nuclepore filters affords the differentiation of nannoplanktonic cells from non-living debris and detritus, thereby holding promise for ecological studies of natural waters.