Submitted to: Mycologia
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/13/2006
Publication Date: 12/15/2006
Citation: Suh, S., Blackwell, M., Kurtzman, C.P., Lachance, M. 2006. Phylogenetics of Saccharomycetales, the ascomycete yeasts. Mycologia. 98(6):1008-1019. Interpretive Summary: Yeasts are of major importance to industry (baked goods, beverages, fuel alcohol, organic acids), to biotechnology (recombinant human insulin, biomass conversion), to medicine (80% of clinical mycotic infections are caused by yeasts) and to agriculture (food spoilage, pest biocontrol). Understanding genetic relationships among yeasts is essential for identification and for prediction of various properties and capabilities. In the present study, multigene DNA sequence comparisons were made of the major yeast groups to provide an understanding of relationships. The result is that this work showed greater diversity among groups than was expected, and it showed that the present system of classification is often incorrect.
Technical Abstract: Ascomycete yeasts (Phylum Ascomycota: Subphylum Saccharomycotina: Class Saccharomycetes: Order Saccharomycetales) comprise a monophyletic lineage with a single order of about 1000 known species. These yeasts live as saprobes, often in association with plants, animals, and their interfaces. A few species account for most human mycotic infections, and fewer than ten species are plant pathogens. Yeasts are responsible for important industrial and biotechnological processes including baking, brewing, and the synthesis of recombinant proteins. Species such as Saccharomyces cerevisiae are model organisms in research, some of which has led to a Nobel Prize. Yeasts usually reproduce asexually by budding, and their sexual states are not enclosed in a fruiting body. The group also is well defined by synapomorphies visible at the ultrastructural level. Yeast identification and classification have changed dramatically with the availability of DNA sequencing. Species identification now benefits from a constantly updated sequence database and no longer relies on ambiguous growth tests. A phylogeny based on single gene analyses has shown the order to be remarkably divergent despite morphological similarities among members. The limits of many previously described genera are not supported by sequence comparisons, and multigene phylogenetic studies are underway to provide a stable circumscription of genera, families, and orders. One recent multigene study has resolved species of the Saccharomycetaceae into genera that differ markedly from those defined by analysis of morphology and growth responses, and similar changes are likely to occur in other branches of the yeast tree as additional sequences become available.