Nomenclature of Microorganisms

Carl Linnaeus developed the system for naming organisms in 1735. This system is referred to as binominal nomenclature. Each organism is assigned two Latinized named because Latin or Greek was the traditional language used by scholars. The first name is called the genus. The second name is called specific epithet, which is the name of the species, and it is not capitalized. The genus and the epithet appear italicized.

Sometimes an organisms named after a researcher, as in the case with Escherichia coli, better known as (E. coli.) The genus is Escherichia, which is named after Theodor Escherich, a leading microbiologist. The epithet or species is coli, which implies that the bacterium lives in the colon.

Organisms were classified into either the animal kingdom or the plant kingdom before the scientific community discovered microorganisms in the seventeenth century. It was at that time when scientist realized that this classification system was no longer valid. Carl Woese developed a new classification system that arranged organisms according to their molecular characteristics and then cellular characteristics. However, it wasn’t until 1978 when scientists could agree on the new system for classifying organism, and it took 12years after this arrangement before the new system was published.

Woese devised three classification groups called domain. A domain is larger than a kingdom. These are:


  • Eubacteria: Bacteria that have peptidoglycan cell walls. (Peptidoglycan is the molecular structure of the cell walls of eubacteria which consists of Nacetyglucosamine, N-acetylmuramic acid, tetrapeptide, side chain and murein.)
  • Archaea: Prokaryotes that do not have peptidoglycan cell walls
  • Eucarya: Organisms from the following kingdoms:


  • Protista: Examples- Algae, protozoa, slime, molds.
  • Fungi: Examples- one-celled yeasts, multicellular molds and mushrooms.
  • Plantae: Examples- moss, conifers, ferns, flowering plant, algae.
  • Animalia: Examples- insects, worms, sponges and vertebrates.

Size of microorganism

Microorganisms are measured using the metric system. In order to give you some idea of the size of a microorganism, let’s compare a microorganism to things that are familiar to you.

A human red blood cell -100 micrometers (μm)

A typical bacterium cell -10 micrometers (μm)

A virus  -10 nanometers (nm)

An atom – 0.1 nanometers (nm)