Definition and Introduction
“Nomenclature” is a Latin word which can be further dissected into two more Latin words namely ‘nomen’ which means ‘name’ and ‘calare’ which means ‘to call’. So Nomenclature is simply referred to as naming things traditionally. A more precise definition would be “the branch of taxonomy which deals with assigning names to taxonomic groups in conformity with published rules”.
Nomenclature is closely associated to the system of classification as these scientific names are extracted from the classification scheme. Each organism has officially only one recognized name which came into being by international agreement. The prevalent system of assigning scientific names to organisms is binomial nomenclature.
Progressive History of Nomenclature:
As this particular piece of writing is strictly confined to Microbiology so the total emphasis would be on the bacteriological or microbial nomenclature.
Early on polynomial (many names) system was used to designate an organism according to their attributes but that system was way much confusing. For example, European honey bee was named as Apis pubescens thorace subgriseo abdomen fusco pedipus posticus glabris utrinque margine ciliatis. In comparison the simple binomial for honey bee is Apis mellifera as regarded by Linnaeus.
The Latin binomial was first coined by a Swedish botanist, Carolus Linnaeus in the middle 1700’s. In his book Systema Naturae which means ‘The Natural Classification’ published in 1735, he tried to classify all living organisms. The binomial (two words/names) which was usually derived from Greek or Latin languages. Linnaeus is often regarded as the “Father of Modern Taxonomy”. Linnaeus’s system of classification is still prevalent today.
David Hendricks Bergey was the first to devise a classification system for bacterial species in 1923. Bergey’s Manual of Systematic Bacteriology (2nd edition) is of prime importance as it contains the proper classification of Bacteria and Archaea.
Bacterial nomenclature was initially open to debate at the first International Congress of Microbiology held in Paris during 1930. The idea for the preparation of lists comprising of names of microbial genera and publications of International Rules of Nomenclature of Bacteria was proposed at the fourth International Congress of Microbiology in Copenhagen, 1947. As for the code, revisions and emendations were made until the present form i.e. the International Code of Nomenclature of Bacteria (ICNB) which was published in 1975 and was revised in 1992(Sneath, 1992). Alterations and amendments can only be made by the by International Committee of Systematic Bacteriology.
Codes of Nomenclature:
Nomenclature codes or Codes of Nomenclature are different rulebooks that govern biological taxonomic nomenclature. Some of the important codes that are internationally accepted are given below.
- International Code of Nomenclature of Prokaryotes (ICNP) formerly called International Code of Nomenclature of Bacteria (ICNB) regulates the nomenclature of Bacteria and Archeae.
- The International Code of Nomenclature for algae, fungi, and plants (ICN) formerly called the International Code of Botanical Nomenclature (ICBN) governs the various set of rules for naming different fungus and algae species.
- International Committee on Taxonomy of Viruses (ICTV) deals with the governance of viruses name.
Binomial nomenclature or Binomial system of classification is a formal system of assigning names to living organisms composed of two parts. It is simply called as binomen or scientific name. As the word binomial which is Latin in origin means ‘‘two part name’’, so binomial nomenclature is simply a system of classification in which an organism is assigned a name comprising of two parts, the first part consists of the Genus (which is usually a noun) to which the microbe or any other organism belongs and second part comprises of a specific epithet (usually an adjective) that further describes the qualities of the generic name. As a whole, these two words account for a species name and are usually derived from Latin and Greek languages.
For example, the common human microbiome, Escherichia coli found in the gut. The first part of the binomial, Escherichia, is the name of the genus to which this microbe belongs and the second part or the specific epithet is, coli, an attribute which is derived from the word colon from where it was found the very first time.
Species vs. Specific epithet:
The fundamental rank of classification is regarded as the species which can be defined as “a group of closely related organisms that can interbreed”. But in case of microbes if 70% of the DNA (Hereditary material) of both the organisms is identical then they are regarded as the same species. Species is a concept and should not be confused with the specific epithet whereas the binomial is simply a label given to the species. For example, it is incorrect to say that Treponema is the genus and pallidum is the species.
How these Names Came into Being?
One may think how these tongue twisting and difficult to pronounce binomials came into being?? The answer to this lies in the following paragraph which contains the sources from which the microorganisms acquire their name.
The name of the microbe can be descriptive. For example,
- Staphylococcus aureus (Staphylo means “cluster” and cocci mean “berry/sphere” like so these are clusters of spheres which are golden in color).
- Streptococcus viridians (Strepto means “chains” so these are chains of spheres and are green in colony color)
- Proteus vulgaris (first and common).
- Helicobacter pylori (spiral/helical rod shaped at the opening to the duodenum).
Named after Scientists:
- Escherichia coli was named after Theodore Escherich who was the first to isolate these bacterial cells from the feces of the infant in 1885. This microbiome resides in the colon of the human.
- Neisseria gonorrhoeae, after Albert Neisser who discovered this in 1879. This microbe cause STD named as gonorrhea which is also mentioned in the specific epithet.
- Some Genera, for example, Erlichia, Pasturella, Listeria are named after Paul Erlich, Louis Pasteur and Joseph Lister respectively.
- The genus Antarctobacter (Antarctica)
- Myobacterium genavense (Geneva, Switzerland)
- Pasturella tularensis (Tulare County, California)
- Legionella longbeachia ( Long Beach, California)
- Pseudomonas fairmontensis (Fairmount Park, Pennsylvania)
Quality/ Attribute of Microbe:
- Saccharomyces cerevisiae which was observed by Theodor Schwann in 1837. Saccharomyces (Sacchro means “sugar” and myces means “fungus”) is a yeast cell that converts grape juice (sugar) into alcohol and cerevisiae (derived from cerevisia meaning “beer”) describes the use of yeast in making beer.
- The largest known bacterium Thiomargarita namibiensis has a special attribute that Thiomargarita meaning “Sulfur pearl” contains microscopic granular sulfur that scatter the incident light and thus providing a glowy pearl like appearance to the cell and namibiensis ( of Namibia) depicts its specific epithet.
- Another bacterium that develop on agar as yellowish colonies contains slime producing spheres, Myxococcus Xanthus ( myxo meaning “slime” and xantho meaning “yellow”).
- Cedecea from CDC (Centers for Disease Control) in USA.
- Legionella ( American Legion)
- Afpia felis ( Air force Institute of Pathology)
- Ideonella (Ideon Research Center) in Lund University, Sweden.
Rules for Binomial Nomenclature:
Following are some rules and conventions to write the accurate binomials or scientific names for organism.
1. When to use Capital letter ( Upper case):
One thing should always be kept in mind that the initials of the generic name are always written with a capital letter (Upper case) and the species name is never written with the upper case. It is always written with a lower case.
For Example, Treponema pallidum
2. When to write in Italics:
The scientific name of the microbe is always written in italics script in printed form and it should be underlined if handwritten. Strain designations and numbers are not italicized though. In a case if all the surrounding text is in italics then the binomial would be non- italic or underlined. For example, the transmission of Yesrinia pestis is accomplished by a vector that is Oriental rat flea.
3. Use of Initials:
Generic name is always written before the specific epithet in full form the very first time it is used in a specific piece of writing. After that, the abbreviations of the generic names that would be the initial capital letters of the generic name should be used to refer the genus. One thing should be kept in mind that the generic initials should not be confusing to other the genera used in the same paper. For example, Entamoeba histolytica is an anaerobic protozoan and E. histolytica can be diagnosed by stool samples.
4. Common name vs. Scientific Name:
In contrast to the scientific names or more precisely when referring to the Genera the common (vernacular) names should always be in lower case and in non-italicized.
For example, Streptococcus pneumoniae is sometimes also called as Pneumococcus.
5. Species and Sub Species Abbreviations:
Species and Sub Species are abbreviated as “sp.” and “subsp.” respectively. Care should be taken that these abbreviations are not italicized. For example, Clostridium sp. and Salmonella enterica subsp. arizonae
6. Plural Forms:
- Plural form of genus is genera
- Species (sp.) is species (spp.)
- Plural of bacillus is bacilli
- Plural of Streptococcus is Streptococci
- Plural of Protozoan is Protozoa
7. Conventions for writing Serovars:
- Serovars are the distinct variations within a species of bacteria or viruses. It is also referred to as serotype. The difference is basically based on the antigens.
- Serovars are always written in Roman type with the initial letter capitalized.
For example, Salmonella enterica serovar Dublin. The serovar can be written without the specific epithet after the first time, like, Salmonella serovar Dublin.
Principles by International Code of Nomenclature of bacteria (ICNB):
Some of the principles as incorporated by the International Code of Nomenclature of bacteria (ICNB) are listed below;
- Each distinctive organism is regarded as species.
- Each organism is given a Latin binomial so as to provide a distinctive international label to the organism.
- The application of names is regulated.
- The oldest available legal name is preferred by the law of priority.
- Labeling of categories is required for classifying organisms.
- Guidance and requirements for valuable publication of new species name are also given.
Importance of Nomenclature:
Nomenclature or more precisely the binomial nomenclature is of prime importance. The introduction of the Latin binomial by Linnaeus was seriously a revolutionary step towards assigning names to organisms.
Advantages of Binomial Nomenclature:
Some of the advantages of binomial nomenclature are provided below
Helps in Communication:
The most vital advantage of binomial nomenclature is the communicative ability. These binomials simply help in communication as these are internationally accepted and used all over the globe.
Confusion or chaos would result if same the same species is designated different names. Common (Vernacular) names can also be cumbersome at times. For example, if the same organism is known as Escherichia coli in one country and Coprobacterium intestinale in the other country serious confusion would result. Binomial nomenclature provides a same platform to the organism and eradicates the uncertainty that can arise if the same organism is studied in different countries.
Surely Better than the Polynomials:
Binomials are far more easy to remember and understand in comparison to the formerly used polynomials. Polynomials were cumbersome and they could be swayed very easily by different taxonomists around the globe. For example, The European honey bee once had a 12 part polynomial, Apis pubescens thorace subgriseo abdomen fusco pedipus posticus glabris utrinque margine ciliatis. In contrary to the binomial Apis mellifera that is far much easier to pronounce and remember.
Beside the binomials are easy to understand and remember they are descriptive as well. For example, Thiomargarita namibiensis, Thiomargarita meaning “Sulfur pearl” contains microscopic granular sulfur that scatter the incident light and thus providing a glowy pearl like appearance to the cell and namibiensis ( of Namibia) depicts its specific epithet. Thus the binomial name also provides a descriptive nature.
Grouping and Classification:
It is through binomial nomenclature we can relate different organisms. By knowing the generic name one can access the family tree of particular organisms. For example, the genus Streptococcus contains multiple species like Streptococcus pneumonia, Streptococcus viridians, Streptococcus vestibularis etc.
Limitation of Binomial Nomenclature:
Binomial nomenclature is the most accepted system of nomenclature but sometimes there is a need of use of Trinomial system.
- Trinomial System of classification is required in certain cases in order to mention the sub-species of the particular organism. For example, Salmonella typhi arizonae is a trinomial name and arizonae is the subspecies.
Attempt an online quiz on Nomenclature and its importance in microbiology here.
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2. Fergus Priest and Brain Austin, Modern Bacterial Taxonomy, 2nd Edition, Chapman and Hall publishers, 1993, Page 135,136.
3. I. Edward Alcamo, Microbes and society: An introduction to microbiology, Jones and Bartlett publishers, INC, 2003, Page number 31, 32.
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5. Naming Conventions by Jay Hardy.
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7. Alcamo’s Fundamental of Microbiology, Jeffrey C. Pommerville, 9th edition, Jones and Bartlett publishers, 2010, Page number 78, 79.
8. Terms Used In Bionomenclature, Compiled by David L. Hakwsworth, Published by Global Biodiversity Information Facility, Copenhagen, 2010, Page no 103, 104.
9. Prescott, Harley, and Klein’s Microbiology, Joanne M. Wiley, Linda M. Sherwood, Christopher J. Woolverton, 7th edition, Tata McGraw-Hill publishers, 2008, Page no.478.
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