[Cytology of the dynamics of capsule formation in yeasts]

Changes in the dimensions and structure of capsules were examined using optical and electron microscopy in the yeast Cryptococcus magnus producing extracellular polysaccharides in the course of its batch cultivation. The mean thickness of capsules was minimal in the period of active budding, but is rapidly increased later on. The dimensions of capsules, as well as the distribution density of capsule fibrils, were maximal at the beginning of the stationary growth phase. The results indicate that the intensive process of capsule formation occurs in formed buds, young separated cells. They contain the greatest number of vesicles with fibrillar material moving from the centre of the cell toward its periphery. The vesicles are absent in the stationary growth phase when the capsules thicken on more. In the phase of dying off, the capsule size and the density of capsule fibres decrease because the capsule material dissolves in the medium. These findings are discussed in relation to capsule biosynthesis and production of extracellular polysaccharides by yeasts.