Eubacteria are microscopic single-celled organisms. They are sometimes referred to as the “true bacteria,” differentiating them from Archaebacteria, similar organisms with some significant genetic and lifestyle differences. The vast majority of organisms we think of as “bacteria” are Eubacteria, with their Archean cousins preferring extreme living environments like nuclear power plants and hydrothermal vents.

In order to delve into the definition of Eubacteria, it is first necessary to discuss a detail of scientific classification. The Eubacteria are at the heart of a serious debate in scientific classification which is reshaping the traditional hierarchy of “Kingdom, Phylum, Class, Order, Family, Genus, and Species.” Originally, Eubacteria were considered part of the Prokaryota kingdom, sometimes called “Monera,” along with their relatives the Archaebacteria.

Prokaryotic organisms like bacteria are primarily defined by their lack of cell nucleus. This makes them evolutionarily distinct from other living organisms, and has led to a number of innovative adaptations. Many prokaryotes are also single-celled, although this is not necessarily a requirement for membership in this kingdom. In addition to the Prokaryota kingdom, biologists also classified organisms into Animalia, Fungi, Plantae, and Protista.

In the 20th century, some people began to argue that Eubacteria and Archaebacteria should be considered two separate kingdoms, reflecting their considerable divergence. Therefore, some textbooks began to print a list of six kingdoms, rather than five. In 1990, the three-domain system was proposed, with researchers suggesting that a biological classification above “kingdom” needed to be created. In the three-domain system, organisms are classified as Eukaryota, Archaea (the new term for Archaebacteria), or Bacteria (the new title for Eubacteria).

Basically, the terms “Eubacteria” and “Bacteria” are interchangeable, since they both refer to a huge collection of organisms found everyone on Earth, from the kitchen floor to mountain streams. However, some scientists prefer one term over the other, reflecting their position on scientific classification. The three-domain system is gaining considerable ground, so people may want to get used to calling “Eubacteria” by their new official title.

Bacteria are so diverse that it is extremely hard to make sweeping generalizations about this domain (or kingdom) of organisms, short of the statement that they are single-celled prokaryotic organisms. They come in a wide assortment of shapes, from neat rods to crazily twisted spirals, and they have a number of functions on Earth. Many people are familiar with bacteria in the form of organisms which cause disease, but bacteria are far more complex than that, and they are likely to endure on Earth long after other forms of life have vanished.