This article is about the microorganisms. For the genus, see Bacterium (genus). For other uses, see Bacteria (disambiguation).
Bacteria
Temporal range: Archean–Present 3500–0 Ma
Pha.
Proterozoic
Archean
Had.
[1]
Scanning electron micrograph of Escherichia coli rods
Scientific classification
Domain:
Bacteria Woese et al. 1990
Phyla
See § Phyla
Synonyms
"Bacteria" (Cohn 1872) Cavalier-Smith 1983
"Bacteria" Haeckel 1894
"Bacteria" Cavalier-Smith 2002
"Bacteriaceae" Cohn 1872a
"Bacteriobionta" Möhn 1984
"Bacteriophyta" Schussnig 1925
"Eubacteria" Woese and Fox 1977
"Neobacteria" Möhn 1984
"Schizomycetaceae" de Toni and Trevisan 1889
"Schizomycetes" Nägeli 1857
Bacteria (/bækˈtɪəriə/ⓘ; sg.: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit soil, water, acidic hot springs, radioactive waste, and the deep biosphere of Earth's crust. Bacteria play a vital role in many stages of the nutrient cycle by recycling nutrients and the fixation of nitrogen from the atmosphere. The nutrient cycle includes the decomposition of dead bodies; bacteria are responsible for the putrefaction stage in this process. In the biological communities surrounding hydrothermal vents and cold seeps, extremophile bacteria provide the nutrients needed to sustain life by converting dissolved compounds, such as hydrogen sulphide and methane, to energy. Bacteria also live in mutualistic, commensal and parasitic relationships with plants and animals. Most bacteria have not been characterised and there are many species that cannot be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology.
Like all animals, humans carry vast numbers (approximately 1013 to 1014) of bacteria.[2] Most are in the gut, though there are many on the skin. Most of the bacteria in and on the body are harmless or rendered so by the protective effects of the immune system, and many are beneficial,[3] particularly the ones in the gut. However, several species of bacteria are pathogenic and cause infectious diseases, including cholera, syphilis, anthrax, leprosy, tuberculosis, tetanus and bubonic plague. The most common fatal bacterial diseases are respiratory infections. Antibiotics are used to treat bacterial infections and are also used in farming, making antibiotic resistance a growing problem. Bacteria are important in sewage treatment and the breakdown of oil spills, the production of cheese and yogurt through fermentation, the recovery of gold, palladium, copper and other metals in the mining sector, as well as in biotechnology, and the manufacture of antibiotics and other chemicals.
Once regarded as plants constituting the class Schizomycetes ("fission fungi"), bacteria are now classified as prokaryotes. Unlike cells of animals and other eukaryotes, bacterial cells do not contain a nucleus and rarely harbour membrane-bound organelles. Although the term bacteria traditionally included all prokaryotes, the scientific classification changed after the discovery in the 1990s that prokaryotes consist of two very different groups of organisms that evolved from an ancient common ancestor. These evolutionary domains are called Bacteria and Archaea.[4]
^"31. Ancient Life: Apex Chert Microfossils". www.lpi.usra.edu. Retrieved 12 March 2022.
^Sender R, Fuchs S, Milo R (19 August 2016). "Revised Estimates for the Number of Human and Bacteria Cells in the Body". PLOS Biology. 14 (8): e1002533. doi:10.1371/journal.pbio.1002533. ISSN 1545-7885. PMC 4991899. PMID 27541692.
^Cite error: The named reference McCutcheon was invoked but never defined (see the help page).
Bacteria (/bækˈtɪəriə/ ; sg.: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large...
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vitamin K2 or by preventing the colonization of the intestine by pathogenic bacteria. These mutually beneficial relationships between E. coli and humans are...
oxygenated environment. Anaerobes may be unicellular (e.g. protozoans, bacteria) or multicellular. Most fungi are obligate aerobes, requiring oxygen to...
Magnetotactic bacteria (or MTB) are a polyphyletic group of bacteria that orient themselves along the magnetic field lines of Earth's magnetic field. Discovered...
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Exogenous bacteria are microorganisms introduced to closed biological systems from the external world.[citation needed] They exist in aquatic and terrestrial...
green sulfur bacteria are a phylum, Chlorobiota, of obligately anaerobic photoautotrophic bacteria that metabolize sulfur. Green sulfur bacteria are nonmotile...
methanogens lack peptidoglycan, a polymer that is found in the cell walls of Bacteria. Instead, some methanogens have a cell wall called pseudopeptidoglycan...
(bacilli) or spherical (cocci) bacteria that share common metabolic and physiological characteristics. These bacteria, usually found in decomposing plants...
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