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United States Department of Agriculture

Agricultural Research Service

Title: Classification of Ascomycetous Yeasts - from Classical to Molecular Approaches

Author
item Kurtzman, Cletus

Submitted to: Meeting Abstract
Publication Type: Other
Publication Acceptance Date: August 2, 2003
Publication Date: N/A

Technical Abstract: Phenotypic characters used for classification of ascomycetous yeasts include type of vegetative reproduction (multilateral budding, bipolar budding, fission, presence or absence of pseudohyphae and true hyphae), ascospore shape (spherical, hat-shaped, dart-shaped, saturn-shaped, roughened, ridged), deliquescence of the ascus, fermentation of sugars, and the utilization of nitrate. Species assigned to the anamorphic genus Candida form pseudohyphae whereas those species previously assigned to Torulopsis do not. Nuclear DNA reassociation studies have shown that this character is strain variable, resulting in Torulopsis being considered a synonym of Candida. DNA reassociation studies also provided evidence that nitrate utilization, glucose fermentation and many other physiological characters are often strain-specific rather than being of phylogenetic significance. As a result, many of the commonly known genera, such as Hansenula, Nematospora, and Wingea have been abandoned as invalid. Gene sequence comparisons have prompted redescription of many current genera and the description of numerous new genera. Major impacts of molecular comparisons are the recognition that budding ascomycetous yeasts are members of a single clade, which is sister to the euascomycetes, that the fission yeasts are a basal group, the bringing together into genera species that are members of the same genetic lineage, placement of anamorphic species with their relatives in teleomorphic genera, and the ability to predict genetic properties of species from their phylogenetic placement. Phylogenetic analyses have also provided an estimate of biological diversity among the yeasts.

Last Modified: 12/19/2014
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