Budding Morphology of a PsychrophilicCryptococcusand Related Species Compared withLeucosporidium Scottii

Abstract

SUMMARY Cryptococcus bhutanensis, C. himalayensis and C. vishniacii are anamorphic basidiomycotinous yeasts. Cryptococcus bhutanensis and C. vishniacii are the first such reported to lack extracellular urease. The budding characters of these three species occur in an association here described for the first time in yeasts. Budding is monopolar and repetitive through the site of the birth scar. The primary bud is holoblastic, secondary buds enteroblastic and continuous with the inner wall layer of the entire parental cell. Septum formation occurs at or slightly above the level of any previously formed collar (bud scar). The Cryptococcus species, budding monopolarly, have a higher width:length ratio (0.70 to 0.83) than the bipolarly budding Leucosporidium scottii (0.55), in which primary buds are distal to the birth scar. Surface topography reflects the degree of cell encapsulation, but appears to result in part from artifacts of capsule collapse during drying in thinly encapsulated cells. Size, shape, surface topography and the details of budding observable with scanning and transmission electron microscopy are major descriptors of yeast cells, particularly valuable for yeasts which fail to reproduce sexually. A list of the budding characteristics which have been useful at various hierarchical levels in systematic schemes as well as in ontological studies (see 13, 21) should include the relative age of primiparous cells, the sites of primary and successive buds, the relation of budding sites to cell shape, the origin of the bud cell wall, septum formation and partitioning, and the resultant appearance of bud and birth scars. Despite this, size is frequently not described in statistical terms, shape is rarely described quantitatively, and there are few yeasts other than Saccharomyces cerevisiae Hansen for which available evidence yields an inclusive picture of the budding process. We here report morphological investigations of an ecologically interesting group of yeasts, psychrophiles or psychrotrophs isolated