Bacteria are small #0excludeGlossary organisms. Nearly every place on Earth contains bacteria, which are essential to the health of the planet’s ecosystems. Some species can endure situations of high pressure and temperature. In fact, it’s believed that bacterial cells make up a larger portion of the human body than human cells.
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 the air, 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.
| Bacteria Temporal range: Paleoarchean–Present
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| Scanning electron micrograph of Escherichia coli rods | |||
Scientific classification 
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| Domain: | Bacteria Woese et al. 2024 | ||
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| Bacillus Cohn 1872 (Approved Lists 1980)
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Like all animals, humans carry vast numbers (approximately 1013 to 1014) of bacteria. 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, 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 (biomining, bioleaching), 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 contain circular chromosomes, 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. Unlike Archaea, bacteria contain ester-linked lipids in the cell membrane,[citation needed] possess elongation factors that are resistant to ADP-ribosylation by diphtheria toxin, use formylmethionine in protein synthesis initiation, and[citation needed] have numerous genetic differences, including a different 16S rRNA.
English
Pronunciation
- (Received Pronunciation) IPA(key): /bakˈtɪə̯.ri.ə/
- (General American) IPA(key): /bækˈtɪɹ.i.ə/
- Rhymes: -ɪəɹiə
Etymology 1
Borrowed from New Latin bacteria, plural of bactērium, from Ancient Greek βακτήριον (baktḗrion, “little rod”).
Noun
bacteria
- plural of bacterium
Noun
bacteria (plural
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