Bacteria

Bacteria are ubiquitous, mostly free-living organisms often consisting of one <a href="/facts/Cell_(biology)/bLM9UQvy">biological cell</a>. They constitute a large <a href="/facts/Domain_(biology)/RpP6V7n6">domain</a> of <a href="/facts/Prokaryote/oYyvaDDH">prokaryotic</a> <a href="/facts/Microorganism/pysJYcE2">microorganisms</a>. Typically a few <a href="/facts/Micrometre/7eDFxD2L">micrometres</a> in length, bacteria were among the first life forms to appear on <a href="/facts/Earth/HLLmDfj0">Earth</a>, and are present in most of its <a href="/facts/Habitat/zo1DN2gA">habitats</a>. Bacteria inhabit the air, soil, water, <a href="/facts/Hot_spring/YrzFykH1">acidic hot springs</a>, <a href="/facts/Radioactive_waste/MjYh5tlu">radioactive waste</a>, and the <a href="/facts/Deep_biosphere/K8wlFPzV">deep biosphere</a> of <a href="/facts/Earth%2527s_crust/VSy2u31r">Earth's crust</a>. Bacteria play a vital role in many stages of the <a href="/facts/Nutrient_cycle/S57nuGbQ">nutrient cycle</a> by recycling nutrients and the <a href="/facts/Nitrogen_fixation/TeLoBpWS">fixation of nitrogen</a> from the <a href="/facts/Earth%2527s_atmosphere/FV97Am25">atmosphere</a>. The nutrient cycle includes the <a href="/facts/Decomposition/6Bve4pgl">decomposition</a> of <a href="/facts/Cadaver/g3SzbFxy">dead bodies</a>; bacteria are responsible for the <a href="/facts/Putrefaction/VmJB2XDh">putrefaction</a> stage in this process. In the biological communities surrounding <a href="/facts/Hydrothermal_vent/0xPqNUkY">hydrothermal vents</a> and <a href="/facts/Cold_seep/fqLSaQXD">cold seeps</a>, <a href="/facts/Extremophile/JGk1eYCk">extremophile</a> bacteria provide the nutrients needed to sustain life by converting dissolved compounds, such as <a href="/facts/Hydrogen_sulphide/UbCqjMMk">hydrogen sulphide</a> and <a href="/facts/Methane/kBHneYnh">methane</a>, to energy. Bacteria also live in <a href="/facts/Mutualism_(biology)/29hCDDS2">mutualistic</a>, <a href="/facts/Commensal/KnJkboX0">commensal</a> and <a href="/facts/Parasitic/HWPcgky7">parasitic</a> relationships with plants and animals. Most bacteria have not been characterised and there are many species that cannot be <a href="/facts/Microbiological_culture/y3VaXn9Q">grown</a> in the laboratory. The study of bacteria is known as <a href="/facts/Bacteriology/51CGDSh6">bacteriology</a>, a branch of <a href="/facts/Microbiology/k7udsq81">microbiology</a>.
Like all animals, humans carry vast numbers (approximately 1013 to 1014) of bacteria. Most are in the <a href="/facts/Gut_flora/Xy1IWzSP">gut</a>, 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 <a href="/facts/Immune_system/HRCTf1pb">immune system</a>, and many are <a href="/facts/Probiotic/gQNAN6ly">beneficial</a>, particularly the ones in the gut. However, several species of bacteria are <a href="/facts/Pathogenic_bacteria/X5QcVN5j">pathogenic</a> and cause <a href="/facts/Infectious_disease/182XrncP">infectious diseases</a>, including <a href="/facts/Cholera/rk8JfWEp">cholera</a>, <a href="/facts/Syphilis/fdnGLyLT">syphilis</a>, <a href="/facts/Anthrax/svk0t5G4">anthrax</a>, <a href="/facts/Leprosy/FSjTpMEB">leprosy</a>, <a href="/facts/Tuberculosis/ggPyovAl">tuberculosis</a>, <a href="/facts/Tetanus/1vukLxUU">tetanus</a> and <a href="/facts/Bubonic_plague/N9dCQ3EP">bubonic plague</a>. The most common fatal bacterial diseases are <a href="/facts/Respiratory_infection/lLKXWrJf">respiratory infections</a>. <a href="/facts/Antibiotic/sF1kIfxg">Antibiotics</a> are used to treat <a href="/facts/Infection/182XrncP">bacterial infections</a> and are also used in farming, making <a href="/facts/Antibiotic_resistance/jsbAywgx">antibiotic resistance</a> a growing problem. Bacteria are important in <a href="/facts/Sewage_treatment/bqLgnLnJ">sewage treatment</a> and the breakdown of <a href="/facts/Oil_spill/A1KGmKI6">oil spills</a>, the production of <a href="/facts/Cheese/JrG8nGCm">cheese</a> and <a href="/facts/Yogurt/JoQjepa7">yogurt</a> through <a href="/facts/Fermentation_(biochemistry)/rxaDr28b">fermentation</a>, the recovery of gold, <a href="/facts/Palladium/P7y0ESWf">palladium</a>, copper and other metals in the mining sector (<a href="/facts/Biomining/oE63gTTV">biomining</a>, <a href="/facts/Bioleaching/1FPuznKK">bioleaching</a>), as well as in <a href="/facts/Biotechnology/8eFnI6FB">biotechnology</a>, and the manufacture of antibiotics and other chemicals.
Once regarded as <a href="/facts/Plant/X5BMDMvS">plants</a> constituting the class Schizomycetes ("fission fungi"), bacteria are now classified as <a href="/facts/Prokaryote/oYyvaDDH">prokaryotes</a>. Unlike cells of animals and other <a href="/facts/Eukaryote/SkwyPLMA">eukaryotes</a>, bacterial cells contain circular chromosomes, do not contain a <a href="/facts/Cell_nucleus/D7sFRa3c">nucleus</a> and rarely harbour <a href="/facts/Cell_membrane/vAXSD0DT">membrane</a>-bound <a href="/facts/Organelle/vhDFnGbs">organelles</a>. Although the term bacteria traditionally included all prokaryotes, the <a href="/facts/Taxonomy_(biology)/Qkg8wuyw">scientific classification</a> changed after the discovery in the 1990s that prokaryotes consist of two very different groups of organisms that <a href="/facts/Evolution/qE5amP6a">evolved</a> from an <a href="/facts/Last_universal_common_ancestor/pnpExNAU">ancient common ancestor</a>. These <a href="/facts/Domain_(biology)/RpP6V7n6">evolutionary domains</a> are called Bacteria and <a href="/facts/Archaea/Adxh0aHw">Archaea</a>. Unlike <a href="/facts/Archaea/Adxh0aHw">Archaea</a>, bacteria contain ester-linked lipids in the cell membrane, are resistant to diphtheria toxin, use formylmethionine in protein synthesis initiation, and have numerous genetic differences, including a different 16S rRNA.

Bacteria open-in-new

Bacteria