GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

2. THE POSITION OF MICROORGANISMS IN NATURE

2.1. CLASSIFICATION OF LIVING ORGANISMS

The differences in appearance and Structure between animals and plants, which served as the basis for classifying living things until the last century, are obvious at first glance. The PLANT AND ANIMAL kingdoms could be distinguished quite clearly as long as little was known about microorganisms. For the third kingdom of living organisms—microorganisms—the name protists was proposed (E. Haeckel, 1866).

There are several classifications of living organisms (Figure). The most widely accepted among microbiologists is the Classification presented in the textbook by H. Schlegel [31]. According to this system, there are Three kingdoms of living organisms: plants, animals, and protists. The Kingdom of Protists encompasses organisms that differ from plants and animals by a low level of morphological differentiation, being primarily unicellular forms. Based on cellular structure, protists can be divided into two distinct groups: higher protists, or eukaryotes, whose Cells resemble those of plants and animals (these include Algae, Fungi, and Protozoa); and lower protists, or prokaryotes, which include Bacteria, notably cyanobacteria (blue-green algae). Following the discovery of archaebacteria, prokaryotes are subdivided into archaebacteria and eubacteria. Viruses, as non-cellular forms, stand apart from all other organisms: they are incapable of independent reproduction, which can only take place within living host cells.

According to E. Chatton (1937), all Living organisms are divided into prokaryotes (bacteria) and eukaryotes (protozoa, fungi, microscopic algae, plants, and animals). In 1979, W. Balch proposed separating archaebacteria into a distinct kingdom, meaning that living organisms comprise three domains: eukaryotes, archaebacteria, and eubacteria.

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Classification of living organisms

According to R. Whittaker (1969), There are five kingdoms of living organisms: prokaryotes (bacteria), protists (protozoa), plants, animals, and fungi. Mycologists consider the classification of fungi as a separate kingdom of living organisms to be The most significant achievement of twentieth-century mycology.

In the late 1990s, another classification system was proposed, dividing living organisms into three superkingdoms: acaryotes (non-nuclear), prokaryotes (pre-nuclear), and eukaryotes (true-nuclear). The superkingdom Acaryota includes the kingdom of viruses, the superkingdom Prokaryota comprises the kingdoms of archaebacteria, cyanobacteria, and eubacteria, and the superkingdom Eukaryota encompasses the kingdoms of plants, animals, and fungi.