Electron Micrography of Bud Formation in Metschnikowia krissii

The fine structure of bud formation of Metschnikowia krissii was studied by means of ultramicrotomy and transmission electron microscopy. Bud protrusion and development were observed by scanning electron microscopy. Bud formation in this yeast takes place by an extension of a small localized area of the existing parent wall. The parent cell and its bud are initially separated by the plasmalemma, creating an intercellular site within which the generation of new cell wall (bud and birth scar areas) occurs centripetally. When the dividing wall is complete and new cell wall material is formed, a narrow cleavage plane becomes increasingly defined. This cleavage plane apparently proceeds laterally toward the direction of the existing outer walls which rupture, resulting in the separation of the bud from the parent cell. The bud scar is prominently convex in shape; the birth scar is less conspicuous and initially concave in shape. Comparison of bud formation in M. krissii is made with that observed in Saccharomyces cerevisiae and Rhodotorula glutinis.