GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

8. FUNGI

8.6. PROBLEMS OF MODERN FUNGAL TAXONOMY

Modern fungal Taxonomy is characterized by two main features. First, the Application of Molecular Research Methods has led to the merging of mycology with molecular biology—a transition already well-established in the taxonomy of Viruses and prokaryotes. Second, There is a noticeable resurgence of what might be called "system-building." Over the past few years, a series of new Classification systems or updated versions thereof have been published for Fungi, eukaryotes, and the biological world as a whole.

The adoption of Molecular and genetic techniques (such as DNA and RNA sequencing, notably of the conservative 18S rRNA, restriction fragment length polymorphism, and cellular Protein Electrophoresis) has challenged the traditional Concept of the fungal kingdom as a monophyletic group. Consequently, higher-level taxa previously included in the fungi have been reassigned to other kingdoms in modern classifications. For example, myxomycetes and certain representatives of eumycetes (oomycetes, hyphochytrids) were removed from the kingdom Fungi. Approximately 20,000 species of organisms traditionally regarded as fungi turned out to be "ambiguous taxa," placed by various specialists simultaneously into Fungi, Chromista, Protista (Protoctista), or Animalia. Furthermore, mounting evidence suggests that fungi are more closely related to animals than to plants.

In The system of living organisms proposed by L. Margulis and K.V. Schwartz (1997), which is widely favored among American scientists, myxomycetes, oomycetes, and chytrids are excluded from the kingdom Fungi and transferred to the kingdom Protoctista (Table 8.2).

Class="center">Table 8.2.

Classification of fungi According to the systems of Hawksworth (1995) and Margulis—Schwartz (1997).

The phylum Mycophycophyta (lichens) has been introduced into the kingdom Fungi as an independent taxon. At the same time, recognizing the phylum Deuteromycota as a higher-level taxon is clearly flawed, as modern data show it to be polyphyletic.

T. Cavalier-Smith’s system (1998) proposes dividing the biological world into six kingdoms, five of which comprise eukaryotes (Animalia, Protozoa, Fungi, Chromista, Plantae) and one comprises prokaryotes (Bacteria). The kingdom Fungi underwent the most radical revisions in this system, being subdivided into two subkingdoms (Eomycota and Neomycota), four phyla (Archemycota, Microsporida, Ascomycota, Basidiomycota), and 20 classes (Table 8.3). Myxomycetes, oomycetes, and hyphochytrids were removed from the kingdom Fungi and reassigned to Protozoa and Chromista. A major limitation of Cavalier-Smith’s classification is its taxonomy of basidiomycetes and ascomycetes, which fails to account for 18S rRNA sequence data.

Table 8.3

Cavalier-Smith's Fungal Classification (1998)

Currently, the most well-supported fungal classification is that of D.L. Hawksworth, published in the *Dictionary of the Fungi* (8th edition, 1995). In this classification, myxomycetes are assigned to the KINGDOM PROTOZOA, while oomycetes and hyphochytrids are placed in Chromista. The kingdom Fungi comprises five phyla: Ascomycota, Basidiomycota, Chytridiomycota, Zygomycota, and "Mitotic fungi" (see Table 8.2). The grouping "Mitotic fungi," which lacks formal taxonomic status and nomenclature, encompasses the deuteromycetes.

According to molecular biological and genetic studies, imperfect fungi (Deuteromycetes) do not constitute an independent taxonomic group. They have either lost their sexual stage or represent the anamorphic states of other fungal groups (most likely belonging to Ascomycetes and Basidiomycetes). Consequently, deuteromycetes should be accommodated within their respective fungal classes.