Taxonomy of Microbes or Microorganisms

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Chapter: Pharmaceutical Microbiology : Characterization, Classification and Taxonomy of Microbes

Taxonomy (Greek : taxis = arrangement or order), and nomos = law, or nemein = to distribute or govern) refers to the science or discipline that essentially deals with the logical arrangement of living things into categories. It may also be defined as ‘the laws and principles of classification of living organisms’.


TAXONOMY

 

Taxonomy (Greek : taxis = arrangement or order), and nomos = law, or nemein = to distribute or govern) refers to the science or discipline that essentially deals with the logical arrangement of living things into categories. It may also be defined as ‘the laws and principles of classification of living organisms’.

 

Aristotle—in fact, was the first ever taxonomist in the fourth century BC who painstakingly and meticulously categorized the so-called ‘living objects’ in the universe into almost 500 well defined species of plant and animal kingdoms.

 

Carolus Linnaeus (1735 – 1759) — a renowned Swedish botanist, virtually named a relatively much larger segment of plants and animals and classified them with great skill and wisdom into the two predominant kingdoms, namely : Plantae and Animalia. In reality, Carolus was instrumental in devis-ing the unique ‘Binomial Scheme of Nomenclature’.

 

Ernst H Haeckel — in the year 1866 logistically segregated the ‘microorganisms’ from the existing plant and animal kingdoms. It was Ernst who first and foremost introduced the new terminology Protist exclusively reserved for the microorganisms. He subsequently coined another term Protista to specifically and categorically include algae (microscopic), fungi, and protozoa thereby forming a ‘third kingdom’.

 

Comments : (1) There was disapproval with regard to the inclusion of both bacteria and fungi together in the aforesaid kingdom Protista.

 

(2) Bearing in mind the recent advances in the domain of ‘Cell Biology’, profuse ob-jections were raised pertaining to the two or three kingdom classification schemes as encountered in Protista.

 

Robert H Whittaker (1969) — duly put forward a most scientific, plausible, and logical system of classification of the living organisms which was widely accepted by the modern microbiologists across the world. However, Robert’s system articulately recognizes the five kingdoms applicable to all living things, namely: Monera, Protista, Fungi, Animalia, and Plantae.

 

Monera — predominantly includes bacteria and cyanobacteria.

 

Protista — essentially comprises of eukaryotes and protozoa.

 

Fungi — specifically belongs to the organisms attached to the kingdom of fungi.

 

Animalia and Plantae — particularly include the traditional animals and plants.

 

It is, however, pertinent to mention here some of the main terminologies, one may frequently come across in the proper and elaborated description of the taxonomy of microorganisms, such as: (a) Speciesi.e., the fundamental rank in the classification system; (b) genusi.e., clubbing together of two or more species ; (c) family – i.e., the collection of genera; (d) order – i.e., the collection of families with identical characteristic features ; (e) class – i.e., the arranging together of order ; (f) phylum (or division) – i.e., grouping together of classes; and (g) kingdomi.e., collection of two or more phyla.

 

Taxon, also known as the basic taxonomic group represents the species i.e., a collection of strains with almost similar characteristic features. In usual practice, the microbial species invariably comprise of a specialized typical strain termed as the type strain, along with all other strains which are regarded very much identical to the type strain so as to justify their logical inclusion in the species. In other words, the type strain is symbolized and designated to be the permanent reference specimen for the species. However, it may be stressed that it is not necessarily always the particular strain which happens to be most characterwise typical of all the strains strategically included in the species, whereas it is essentially the specific strain to which all the rest of the strains should be critically compared to ascertain, whether they do have a close resemblance sufficient enough to belong to the same species. The above glaring statement of facts pertaining to the type strains are extremely vital and important; and, therefore, specialized and particular attention need to be given to their genuine and regular mainte-nance as well as preservation. The following are two world famous reference collection centres located in USA and UK, namely:

 

(a) American Type Culture Collection (ATCC), Rockville, Maryland, USA, and

 

(b) National Collection of Type Cultures (NCTC), UK.

 

Interestingly, one may critically observe that the various strains strategically present very much within species may differ slightly from one another in three prominent manners, namely:

 

(a) Biovars: These are variant bacterial strains and are duly characterized by biochemical or physiological characteristics.

 

(b) Morphovars: These are variants within a species defined by variation in morphological characteristics.

 

(c) Serovars: These are variants within a species defined by variation in serological reactions.

 

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