FUNDAMENTALS OF MICROBIOLOGY - V. M. Samygin - 2015

CHAPTER 2. SYSTEMATICS, CLASSIFICATION, AND TAXONOMY OF MICROORGANISMS

Microbiology is primarily concerned with The Study of Bacteria, microscopic (Molds) Fungi, and Viruses. The microbial world is exceptionally diverse: there are over 5,500 species of bacteria and more than 70,000 species of fungi, with these numbers continually growing. Systematics helps us make sense of this immense variety. Its goals are to elucidate evolutionary relationships among various microorganisms, unite them into interconnected and hierarchically subordinated taxa (categories) such as species, genus, family, and so on, establish the foundations of speciation, and ultimately create an ordered system of Classification.

Taxonomy (from the Greek taxis meaning arrangement in order) is the science of the principles and Methods of classifying living organisms in a hierarchical framework. The primary tasks of taxonomy include the comprehensive description and identification of taxonomic units and The Development of a convenient method for arranging these units for classification, which forms an integral part of systematics. The terms "systematics" and "taxonomy" are frequently used as synonyms.

Nomenclature refers to the precise designation of individual taxa based on the binomial principle, comprising the generic and specific names, along with the set of rules for naming taxa and the list of such names. Nomenclature comes into play only after a classification or classification scheme has been developed.

Classification (from the Latin classis meaning rank or group) is The process of dividing a set of organisms into specific taxonomic groups—such as families, genera, species, and variants—based on shared characteristics.

Identification (from the Latin identifico meaning to identify) is the process of determining whether a studied Organism belongs to a particular taxon.

The lowest taxonomic unit in the systematics of microorganisms is the species; species are grouped into genera, followed by families, and so on. Currently, the following hierarchical categories are recognized: kingdom - division - group - Class - order - family - genus - species. To designate a species, the binomial nomenclature proposed by the Swedish scientist Carl Linnaeus (1707–1778) is used. In this system, the first word denotes the genus. It is capitalized and is derived either from a word characterizing a morphological feature or from the surname of the scientist who discovered a species within that genus. The second word is written in lowercase. It represents the species name and is derived from a noun indicating the source of Water/144.html">Origin of the microbe, the type of disease it causes, or other distinguishing characteristics. For example, the CAUSATIVE AGENT OF anthrax is called Bacillus anthracis. This indicates that the microorganism belongs to the genus Bacillus (Latin for rod), meaning spore-forming rod-shaped bacteria, and is the causative agent of anthrax (anthrax denoting the disease).

METABOLISM/2.html">THE CONCEPT OF a "species" can be defined as a population of microorganisms sharing a common origin and genotype, and exhibiting similar morphological and biological properties. To characterize microbial species and differentiate them, scientists use antigenic Structure, PHYSIOLOGICAL AND BIOCHEMICAL properties, and the processes induced by the microbe in its natural habitat. In recent years, with the advancement of molecular biology, new approaches to characterizing microorganisms have been developed, which have profoundly impacted their systematics. In particular, genosystematic methods are of certain value as they allow for the direct characterization of the hereditary properties (genotype) of microorganisms, thereby complementing descriptions based on Structural and functional properties (phenotype).

In microbiology, the terms "strain" and "clone" are widely used. A strain is a narrower concept than a species. A strain is a microorganism isolated from natural sources or obtained artificially. Different cultures or populations of the same species that differ by some minor characteristics are referred to strains. For example, the Influenza virus isolate from Hong Kong is called the "Hong Kong" strain, while those isolated from other parts of Asia are referred to as strains of "Asian" flu. Strains may differ, for instance, in their resistance to drugs or their ability to synthesize specific compounds. However, the Properties of Individual strains do not exceed the BOUNDARIES OF THE species. The word "clone" refers to a culture that is the progeny of a single Cell.

A culture containing microorganisms of only a single species is called a pure culture. Mixed cultures refer to a mixture of heterogeneous microorganisms isolated from natural substrates (water, food products, air, swabs, and so on). If two species of microorganisms grow together in a culture and are purposely maintained in association with one another, such a culture is termed an associated or two-component culture.

Microorganisms vary considerably in their external features, internal structure, and biological properties. They are divided into 3 kingdoms:

- Vira (viruses)

- Eucariotae (eukaryotes)

- Procariotae (prokaryotes).

Eukaryotes include Protozoa (Ciliates, amoebas, microsporidia, trypanosomes) and fungi (molds, Yeasts). Prokaryotes comprise the division of cyanobacteria and eubacteria. The latter, in turn, are subdivided into the orders: true bacteria, rickettsiae, Mycoplasmas, chlamydiae, spirochetes, and actinomycetes (fungus-like bacteria).

The vast majority of microorganisms are unicellular (bacteria, spirochetes, protozoa), but some possess a multicellular structure (molds, yeasts). The primary criterion uniting all The Diversity of microorganisms is their microscopic size, which typically ranges from 0.5–1 µm to 15–20 µm.