Cell agglutination in the yeast, Hansenula wengei, correlated with changes in ultrastructure

The yeast Hansenula wingei exhibits a cellular agglutination of opposite mating types as an early step in sexual reproduction by conjugation. Freshly harvested and washed cells show a low agglutinability in the absence of cations. Previous investigations have shown that cell agglutinability may be activated by either chemical or physical treatments. In this thesis ultrastructure of the cell walls and external fringe, viewed with electron microscopy, is correlated with certain treatments known to affect the agglutinability of the cells. Activation of agglutinability with cations is freely reversible, strictly dependent upon the presence of dissolved salts, and appears to cause no noticable ultrastructural changes in the cell wall or fringe. Activation of agglutinability with brief heat treatment is not freely reversible, but makes the agglutinable state independent of dissolved salts, and appears to remove the fringe material quantitatively from the cell wall surface. Cell agglutination of both heat activated and magnesium activated cells is freely and repeatedly reversible in 8M urea, and this confirms a previously published conclusion that cell agglutination involves weak chemical bonding. Several methods of measuring the intensity of binding and the rates of agglutination show that heat activated cells demonstrate a more intense binding than cation activated cells. The results suggest further that the agglutinative component molecules are located in both the external fringe and the outer layer of the cell wall proper. It is also noted that the mucopolysaccharide specific stain, ruthenium red, is localized in both of these layers.