Bacterial taxonomy is subfield of taxonomy devoted to the classification of bacteria specimens into taxonomic ranks.
In the scientific classification established by Carl Linnaeus, each species is assigned to a genus resulting in a two-part name. This name denotes the two lowest levels in a hierarchy of ranks, increasingly larger groupings of species based on common traits. Of these ranks, domains are the most general level of categorization. Presently, scientists classify all life into just three domains, Eukaryotes, Bacteria and Archaea.
Bacterial taxonomy is the classification of strains within the domain Bacteria into hierarchies of similarity. This classification is similar to that of plants, mammals, and other taxonomies. However, biologists specializing in different areas have developed differing taxonomic conventions over time. For example, bacterial taxonomists name types based on descriptions of strains. Zoologists among others use a type specimen instead.
Diversity
Bacteria (prokaryotes, together with Archaea) share many common features. These commonalities include the lack a of nuclear membrane, unicellularity, division by binary-fission and generally small size. The various species can be differentiated through the comparison of on several characteristics, allowing their identification and classification. Examples include: Phylogeny: All bacteria stem from a common ancestor and diversified since, and consequently possess different levels of evolutionary relatedness (see Bacterial phyla and Timeline of evolution) Metabolism: Different bacteria may have different metabolic abilities (see Microbial metabolism) Environment: Different bacteria thrive in different environments, such as high/low temperature and salt (see Extremophiles) Morphology: There are many structural differences between bacteria, such as cell shape, Gram stain (number of lipid bilayers) or bilayer composition (see Bacterial cellular morphologies, Bacterial cell structure)
History
First descriptions
Bacteria were first observed by Antonie van Leeuwenhoek in 1676, using a single-lens microscope of his own design. He called them "animalcules" and published his observations in a series of letters to the Royal Society.
Early described genera of bacteria include Vibrio and Monas, by O. F. Müller (1773, 1786), then classified as Infusoria (however, many species before included in those genera are regarded today as protists); Polyangium, by H. F. Link (1809), the first bacterium still recognized today; Serratia, by Bizio (1823); and Spirillum, Spirochaeta and Bacterium, by Ehrenberg (1838).
The term Bacterium, introduced as a genus by Ehrenberg in 1838, became a catch-all for rod-shaped cells.
Early formal classifications
Bacteria were first classified as plants constituting the class Schizomycetes, which along with the Schizophyceae (blue green algae/Cyanobacteria) formed the phylum Schizophyta.
Haeckel in 1866 placed the group in the phylum Moneres (from μονήρης: simple) in the kingdom Protista and defines them as completely structureless and homogeneous organisms, consisting only of a piece of plasma. He subdivided the phylum into two groups: (no envelope) Protogenes – such as Protogenes primordialis, now classed as a eukaryote and not a bacterium Protamaeba – now classed as a eukaryote and not a bacterium Vibrio – a genus of comma shaped bacteria first described in 1854) Bacterium – a genus of rod shaped bacteria first described in 1828, that later gave its name to the members of the Monera, formerly referred to as "a moneron" (plural "monera") in English and ""(fem. pl. "") in German Bacillus – a genus of spore-forming rod shaped bacteria first described in 1835 Spirochaeta – thin spiral shaped bacteria first described in 1835 Spirillum – spiral shaped bacteria first described in 1832 etc. (with envelope) Protomonas – now classed as a eukaryote and not a bacterium. The name was reused in 1984 for an unrelated genus of Bacteria Vampyrella – now classed as a eukaryote and not a bacterium
The classification of Ferdinand Cohn (1872) was influential in the nineteenth century, and recognized six genera: Micrococcus, Bacterium, Bacillus, Vibrio, Spirillum, and Spirochaeta.
The group was later reclassified as the Prokaryotes by Chatton.
The classification of Cyanobacteria (colloquially "blue green algae") has been fought between being algae or bacteria (for example, Haeckel classified Nostoc in the phylum Archephyta of Algae).