Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: December 9, 2010
Publication Date: December 9, 2010
Citation: Kurtzman, C.P. 2010. Impact of molecular systematics on the yeasts, a taxonomic study, 5th edition (2010). Meeting Abstract. Technical Abstract: The Yeasts, A Taxonomic Study is the primary taxonomic reference used worldwide for identification and systematics of yeasts. The first edition was authored by J. Lodder and N.J.W. Kreger-van Rij (1952), but subsequent editions have been edited volumes with numerous contributors (editors and dates: J. Lodder, 1970, 2nd edn.; N.J.W. Kreger-van Rij, 1984, 3rd edn.; C.P. Kurtzman and J.W. Fell, 1998, 4th edn.; C.P. Kurtzman, J.W. Fell and T. Boekhout, 2010, 5th edn.). For the 5th edition, there are 76 contributors from 22 countries, including 8 contributors from Japan. Species classification in the 4th edition was somewhat influenced by molecular comparisons, mainly by nuclear DNA reassociation studies and to some extent from D1/D2 nuclear large subunit rRNA gene sequence analysis. Application of gene sequence analyses for species identification became widespread after publication of D1/D2 databases for essentially all described ascomycetous yeasts (Kurtzman and Robnett 1998) and basidiomycetous yeasts (Fell et al. 2000). Following this, many laboratories worldwide utilized and expanded these databases as many new species were described. One impact of this work has been the doubling of described species over the past decade. The 4th edition of The Yeasts, A Taxonomic Study included about 700 species, whereas nearly 1500 species are described in the 5th edition. The impact of molecular comparisons has extended beyond species identification. Gene sequence analyses showed that the budding yeasts (Saccharomycotina) are a sister group to the “filamentous fungi” (Pezizomycotina) and that the Taphrinomycotina, which includes Schizosaccharomyces, Saitoella, Pneumocystis, Protomyces, Taphrina and Neolecta, is basal to the Saccharomycotina and the Pezizomycotina (James et al. 2006; Kurtzman 2010; references therein). Similarly, the Basidiomycota was found to be polyphyletic and gene sequence analyses have divided this major group of fungi into three large clades, the Ustilaginomycotina, the Agaricomycotina and the Pucciniomycotina (James et al. 2006; Boekhout et al. 2010; references therein). All three of these subphyla contain taxa that are classified as yeasts, i.e., asexual reproduction by budding or fission, and sexual states unenclosed in a fruiting body. Molecular analyses have been used to phylogenetically circumscribe genera, resulting in a marked subdivision of such large genera as Saccharomyces and Pichia. The 4th edition included 97 genera, but 150 are given in the 5th edition. Much of the increase in number of genera has been due to reclassification of species following multigene sequence analysis. Despite the strides made in the past decade, much remains to be done. Some of the newly circumscribed ascomycetous genera are clearly divergent and the discovery of new species in these clades may result in future division of some these genera. Datasets including a larger number of gene sequences are needed to resolve relationships among the genera, which may require whole genome sequences to accurately place some of the more divergent taxa. The basidiomycetous yeasts have been characterized from D1/D2, ITS and SSU sequences, but these sequences have insufficient signal to resolve the polyphyly that is apparent from the analyses. Consequently, resolution of basidiomycetous yeasts into phylogenetically circumscribed genera awaits further multigene analyses. Complicating this work is present lack of recognition of which non-yeast taxa are closely related to the yeast taxa and whether, in some cases, the two growth states may be members of the same genus.