Nomenclature and microbial classification

Nomenclature

Each species of microorganism has onlysingle officially accepted the name, by international agreement. This system provides for precise communication. If an organism are to be called Escherichia coli in one country and Coprobacterium intestinal in another, chaos would result. It would be difficult to know that the same organism are being studied.

The name of a species is usually a convenient label. It is not essential even descriptive, although some names are. For example, micrococcus gluteus means “yellow berry” in latin, and proteus Vulgaris is latin for “common organism of many shapes.” Some species are formulated after persons: for example, Escherichia (a german bacteriologist): or Clostridium bakery- the spindle-shaped organism, named after H.A. barker (an American biochemist). Some names are even witout any significance E.g., Rubella slithy formins-“the organism whose shape resembles runes (characteristics of an ancient alphabet) and which is slithy,” the latter term being taken from lewis Carroll's poem “jabberwocky” from Alice in Wonderland. The important point is that names are only convenient designations. For example, instead of referring to “the rod-shaped, acid-fast bacterium that is slow-growing, is stimulated by glycerol, causes pulmonary tuberculosis in humans, is spread mainly by airborne droplets, forms buff-colored colonies, synthesizes niacin, reduces nitrate to nitrate, and is pathogenic for guinea pigs,” it is much more convenient simply to say “mycobacterium tuberculosis.”

Although it might be concluded that microbial names could be constructed almost at random, the fact is that certain rules must be followed. Bacteria, for example, are named according to rules set up in the international code of nomenclature of bacteria; other codes govern the naming of algae, fungi, and viruses.

One lae in bacteriological nomenclature is that a name must be written in a Latin or Latinized binomial (two words) and must follow certain laws of Latin grammar. The first word in the binomial is the genus name and is always capital. The second word is the specific epithet are provided in italics (or underlined, which means “italics” to a printer). Bacteria are moreover referred to by common or colloquial names, which have no official significance in nomenclature and are never italicized ,for example, the “colon bacillus,” which is e. coil, or the “tubercle bacillus,” which is M. tuberculosis. These names do not lead to precise communication; for instance, many bacteria occur in the colon besides E. Coli and other organisms besides M. tuberculosis can cause tuberculosis.

These bacterial names which have been official standing in microbiology were published in the accepted lists of bacterial names in January 1980. Any new or additional names must be published in the International journal of systematic bacteriology in order to achieve official recognition.

The international code of nomenclature of bacteria was founded with reference to the much earlier established International Codes of Zoological and Botanical Nomenclature. All of these codes incorporate certain common principles as listed below.

1. Each distinct type of organism is designated as a species.
2. The species is designated by a Latin binomial to provide a characteristics international label ,binomial system of nomenclature.
3. Rules are established for the application of names.A law of priority ensures the use of the outlet available legitimate name.

4. Designation of categories is essential for classification of organisms.
5. Requirements are given for effective publication of new specific names, as well as guidance in coining new names.

Microbial classification

In microbiology, taxa are initially constructed through strains. A strain is constructed up of all the descendants of a pure culture; it is generally a succession of cultures derived from an initial colony. Each strain has a specific generative evidence and designation.

For example, strain ATCC 19554 is a strain of spirilla isolated originally from pond water in Blacksburg, Virginia in 1955 by Wells and Krieg, and cultures of this strain are kept at the American type culture collection (ATCC), Rockville, Maryland. Cultures of the same species that were isolated from other sources would be considered different stains.

The basic taxonomic group (taxon) is the species i.e., a collection of strains having similar characteristics. Bacterial species consist of a special strain called the kind strain together with all other strains that are considered almost similar to the type strain as to warrant inclusion in the species. The type strain is the strain that is pescribed to be the permanent reference specimen for the species. Unfortunately, it is different always the strain that is most typical of all the strains included in the species, but if it is the strain in which all other strains must be compared to see if these usually resemble it closely enough to belong to the species. Therefore, type strains are particularly essential and special attention is given to their maintenance and preservation, particularly by the national collection of collections such as the ATCC in the United States of the national collection of type cultures in England. Many other culture collections are maintained throughout the world.

In the vocabalary just given for a bacterial species, the phrase “considered almost similar to the type strain” indicates that the definition contains an element of subjectivity. In other words, the criteria which one taxonomist believes to constitute “sufficient similarity” may be quite different from those used by another taxonomist. At present, there are no typical criteria for a bacterial species that are universally accepted. However, certain criteria based on DNA homology experiments are probably more widely accepted today than any others and eventually may lead to a unifying concept for defining a species. Just as a bacterial species is made of a collection of similar strains, a bacterial genus is composed of a collection of similar species. One of the species is designated the type species, and this serves as the permanent example of the genus; that is, other species must be judged to be sufficiently similar to the type of species to be included with it in the genus. Unfortunately, there is even less agreement about the criteria for bacterial genus than there is of a bacterial species. Taxonomic groups of upper rank than genus are listed below, and the same considerations about subjectivity apply here as well:

Family a group of similar genera

Order a group of similar families

Class a group of similar orders

Division a group of similar classes

Kingdom a group of similar divisions

The goals of classification

Taxonomists strive to make classifications that have the following two qualities:

1. Stability: Classifications that are subjected to frequent, radical changes generates to the confusion. Every attempt should be formulated to devise classifications that need only minor changes as new information becomes available.
2. Predictability: By acknowledging the characteristics of one type of a taxonomic group. It should be feasible to predict that the other members of the same type probably have similar characteristics. If this could not be done, the classification has little significance.

References

Arvind, Keshari K. and Kamal K Adhikari. A Textbook of Biology. Vidyarthi Pustak Bhander.

Michael J.Pleczar JR, Chan E.C.S. and Noel R. Krieg. Microbiology. Tata Mc GrawHill, 1993.

Powar. and Daginawala. General Microbiology.

Rangaswami and Bagyaraj D.J. Agricultural Microbiology.