Temporal and Spatial Differences in Cell Wall Expansion during Bud and Mycelium Formation in Candida albicans

Abstract

The infectious yeast C. albicans is capable of growing in either a budding or mycelium form, depending upon the pH of the supporting medium. By monitoring the position of polylysine-coated beads firmly attached to the wall of growing cells, the zones of expansion for the surface of the cell wall were mapped for the alternative growth forms. Both spatial and temporal differences are demonstrated to exist. During roughly the first 2/3 of bud growth, a very small, highly active apical zone accounts for .apprx. 70% of surface expansion. The remaining 30% is due to general expansion. When a bud reaches .apprx. 2/3 of its final surface area, the apical zone shuts down, and subsequent expansion is completed by the general mechanism. During mycelial growth, at least 90% of expansion is due to a small, highly active apical growth zone, and < 10% is due to the general mechanism. In contrast to budding cells, the apical zone of the growing mycelium never shuts down as long as growth continues in the mycelial form. These distinct temporal and spatial differences in expansion are considered in terms of the regulation of alternative phenotypes in Candida.