Wall structure and bud formation inCryptococcus neoformans

Abstract

Cells ofCryptococcus neoformans fixed by the TAPO-acrolein-osmium method show a highly electron-dense capsule with fibrillar and granular structures and a wall organized in two main layers. The outer layer is electrontransparent and contains a variable amount of low to medium-density material, especially abundant in actively growing cells. The inner wall layer shows a lamellar aspect and in the majority of the cells may further be divided into two sub-layers mainly on the basis of lamellar compactness. The wall of the bud, since its early appearance, is also formed by an inner dark lamellar layer and an outer, electron-transparent one. While the former is seen as a direct continuation of the corresponding innermost part of the parent wall, the latter orginates from the inside of the lamellar wall and grows out with the emerging bud through a rupture of the lateral parental wall. Capsular material always covers the wall of the bud even if its amount is very reduced in the early stages of the budding.