GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

9. YEASTS

9.5. TAXONOMY AND SYSTEMATICS OF YEASTS

The first scientific Classification of Yeasts was developed in 1896 by the Danish mycologist E.C. Hansen. He grouped spore-forming yeasts into eight genera within the family Saccharomycetaceae. The most prominent classifications published in the first half of the 20th century were those developed by the Dutch school led by J. Lodder and N.J.W. Kreger-van Rij (1952), and by the Soviet scientist V.I. Kudryavtsev (1954). The former classification was primarily based on the morphological and physiological properties of yeasts, whereas the latter, In addition to these features, took into account the specific habitats of the species and their environmental adaptation. A major milestone in Yeast systematics was the application of genosystematics, which involves The Study of life cycles, mating concepts, and Hybridization. Until recently, most researchers classified yeasts into three subphyla within the division Eumycota (kingdom Mycota): Ascomycotina, Basidiomycotina, and Fungi Imperfecti (Deuteromycotina). Ascomycetes form asci containing endogenous sexual spores, Basidiomycetes produce teliospores and basidia-like sporophores bearing exogenous sexual spores, while deuteromycetes form exclusively asexual spores and lack a sexual reproductive cycle.

In 1984, a classification by N.J.W. Kreger-van Rij was published, which remained the most comprehensive for nearly 16 years (Table 9.1).

Class="center">Table 9.1

Yeast classification (1984)

Similar to the systematics of prokaryotes and micromycetes, the Application of Molecular biology and Genetic Methods in yeast research—such as DNA and RNA sequencing data (particularly regarding the conserved 18S rRNA and specific domains of 28S rRNA), restriction fragment length polymorphism analysis, and cellular Protein Electrophoresis—has challenged the traditional yeast classification.

In 1998, the fourth edition of The Yeasts: A Taxonomic Study, edited by American scientists C.P. Kurtzman and J.W. Fell, was published. According to this edition, asporogenous deuteromycetous yeasts do not constitute an independent taxonomic group, but rather belong to the ascomycetous and basidiomycetous yeasts. In 2000, C.P. Kurtzman published a phylogenetic classification of yeasts (Table 9.2).

Table 9.2

Placement of asporogenous yeasts in Kurtzman's classification (2000)

It should be noted that today the very term "asporogenous" (or imperfect) yeasts is no longer accurate. Because these yeasts have been reassigned to ascomycetes or basidiomycetes, they are presumed capable of sexual reproduction; however, the specific conditions required for their sexual cycle have yet to be identified or established.