MICROBIOLOGY - M.H. Serhiichuk - 2008

CHAPTER 7. MICROBIAL SYSTEMATICS

Taxonomic Terminology

Establishing relationships between phenomena and objects, as well as their identification, is carried out according to certain conventional systems that constitute biological Taxonomy.

The Classification of higher organisms (plants and animals) into taxonomic categories largely reflects their phylogenetic relationships. However, establishing such relationships in the case of prokaryotes is impossible because historical data are fragmentary, which prevents making definitive Conclusions.

Systematics is a branch of theoretical biology, and like any theoretical science, it requires some formalization and definition of terms, primarily such as taxonomy, systematics, and classification.

Taxonomy is the science of biological classification, or in other words, a branch of Organism systematics concerned with establishing the hierarchy of individual microbial taxa. A taxon is a group of organisms that exhibit a specified degree of homogeneity. The tasks solved by taxonomy primarily include classification, nomenclature, and identification.

According to G. Zavarzin, systematics is The Theory of organism diversity that studies the relationships between their groups. Alternatively, systematics can be defined as the distribution (classification) of microorganisms into groups (taxa) based on certain characteristics, as well as the establishment of Phylogenetic relationships among them.

Classification, nomenclature, and identification are three interrelated aspects of microbial systematics. Classification is the arrangement of a multitude of microorganisms with common traits into groups (taxa). Nomenclature is the naming of Bacteria in accordance with international principles, rules, and recommendations that ensure accurate mutual understanding among specialists. Identification is the comparison of unknown (studied) organisms with already classified ones in order to establish their identity and name, i.e., assigning the studied object to a specific taxon.

In microbiology, as in the systematics of higher organisms, the basic taxonomic unit is the species (species) — one of the most debatable concepts in bacteriology. While the definition of "species" in Higher Plants and animals is based on clearly expressed morphological and physiological differences, as well as the inability of representatives of two populations to interbreed, these criteria are not applicable to bacteria because bacteria are morphologically quite uniform and lack a Sexual process in reproduction.

There are several Structure/97.html">Definitions of the bacterial "species" concept. Thus, in 1949, M. Krasilnikov wrote on this subject that a species is a group of related organisms that share a common origin and, at a given stage of evolution, are characterized by certain morphological, biochemical, and physiological traits; they are separated from other species and adapted to a specific habitat. Such a definition is classic from a scientific and philosophical standpoint, but it implies establishing phylogenetic affinity, which is practically impossible to do in the case of bacteria because, unlike vertebrates or plants where paleontological data are successfully used, such data are mostly absent for microorganisms. Genetic material can be exchanged between individual bacterial species of the same or different genera.

According to R. Stanier, "a species is a collection of individuals (and in the case of microorganisms, clonal populations) that exhibit a high degree of phenotypic similarity, but at the same time have noticeable differences from other collections of the same genus." According to the microbiological terminology adopted in Ukraine (DSTU, 1994), METABOLISM/2.html">THE CONCEPT OF "species" is defined as "a taxonomic unit that unites organisms on The basis of morphological, physiological-biochemical, genetic, and other traits."

According to C. Linnaeus's binomial nomenclature, a species name is given in two words in Latin. The genus name is always capitalized. The genus or species name may reflect some characteristic (property), indicate the author who studied it, etc. For example, Bacillus subtilis — hay bacillus; Escherichia coli — colon bacillus; Clostridium pasteurianum — named after the French scientist Pasteur; Escherichia — in honor of the German scientist Escherich; Rickettsia prowazekii — in honor of the Czech scientists Ricketts and Prowazek.

In microbiology, the concept of a "strain" is often used. Different researchers attribute different meanings to this concept. Thus, according to the microbiological terminology of Ukraine, "a strain is a pure culture of a microorganism of any species isolated from a particular source." Often, a strain refers to colonies grown during the plating of an initial culture, or bacterial cultures with certain deviations from the studied one.

According to the rules of bacterial classification, species are grouped into genera, meaning a genus is a group of related species. Similar genera are grouped into families, families into orders, orders into classes, and so on. The largest taxonomic unit is the kingdom; for bacteria, this is the kingdom Procaryotae.