Scanning and transmission electron microscopic studies revealed the presence of slime-like, amorphous material on the surface of Schizosaccahromyces pombe RIVE 4-2-1 cells, independently, whether they were in flocculated or in non-flocculated state. Close contact of the adjacent cells via the merging outermost cell wall layers was found, however, only in the case of floc formation, which was induced by cultivating the cells in the presence of 6% (v/v) ethanol. Irreversible loss of the flocculation ability of the cells by treatment with proteinases suggests that proteinaceous cell surface molecules as lectins contribute to the cell-to-cell interaction during flocculation. Both proteinase K and pronase treatments removed a distinct outer layer of the cell wall, which indicated that the protein moieties of the phosphogalactomannan outer surface layer has a crucial role in the maintenance of cell wall integrity. In the case of lysing enzyme treatment the removal of the outermost layer was also observed as the first step of the cell wall digestion, while driselase treatment resulted in almost complete digestion of the cell wall.

Cell aggregation (flocculation) of the yeast Schizosaccharomyces pombe strain RIVE 4-2-1 developed in glucose-containing medium, but only in the presence of ethanol. Cell surface proteins which participated in cell to cell interactions were characterised by the susceptibility of flocculation to different proteolytic enzymes, heat treatment, denaturing and thiol compounds and by the inhibition of flocculation by sugars and derivatives. It was shown that a galactose-specific lectin was involved in this new type of flocculation.