Bacteria

Bacteria (/bækˈtɪəriə/; singular: bacterium) constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals. Bacteria were among the first life forms to appear on Earth, and are present in most habitats on the planet, growing in soil, acidic hot springs, radioactive waste, water, and deep in the Earth's crust, as well as in organic matter and the live bodies of plants and animals, providing outstanding examples of mutualism in the digestive tracts of humans, termites and cockroaches.

There are typically 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre of fresh water; in all, there are approximately five nonillion (5×1030) bacteria on Earth, forming a biomass that exceeds that of all plants and animals. Bacteria are vital in recycling nutrients, with many steps in nutrient cycles depending on these organisms, such as the fixation of nitrogen from the atmosphere and putrefaction. In the biological communities surrounding hydrothermal vents and cold seeps, bacteria provide the nutrients needed to sustain life by converting dissolved compounds such as hydrogen sulphide and methane. Most bacteria have not been characterised, and only about half of the phyla of bacteria have species that can be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology.

There are approximately ten times as many bacterial cells in the human flora as there are human cells in the body, with large numbers of bacteria on the skin and as gut flora. The vast majority of the bacteria in the body are rendered harmless by the protective effects of the immune system, and a few are beneficial. However, a few species of bacteria are pathogenic and cause infectious diseases, including cholera, syphilis, anthrax, leprosy, and bubonic plague. The most common fatal bacterial diseases are respiratory infections, with tuberculosis alone killing about 2 million people a year, mostly in sub-Saharan Africa. In developed countries, antibiotics are used to treat bacterial infections and in agriculture, so antibiotic resistance is becoming common. In industry, 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, 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 independently from an ancient common ancestor. These evolutionary domains are called Bacteria and Archaea.

Read more about Bacteria:  Etymology, History of Bacteriology, Origin and Early Evolution, Morphology, Metabolism, Growth and Reproduction, Genetics, Classification and Identification, Interactions With Other Organisms, Significance in Technology and Industry

Other articles related to "bacteria":

Bacteria - Significance in Technology and Industry
... Further information Economic importance of bacteria Bacteria, often lactic acid bacteria such as Lactobacillus and Lactococcus, in combination with yeasts and molds, have been used for thousands of years in the ... The ability of bacteria to degrade a variety of organic compounds is remarkable and has been used in waste processing and bioremediation ... Bacteria capable of digesting the hydrocarbons in petroleum are often used to clean up oil spills ...
Antimicrobial Peptides - Activities
... The modes of action by which antimicrobial peptides kill bacteria is varied and includes disrupting membranes, interfering with metabolism, and targeting cytoplasmic components ... to many conventional antibiotics these peptides appear to be bacteriocidal (bacteria killer) instead of bacteriostatic (bacteria growth inhibitor) ...
Black Fly - Ecology
... catching passing debris (small organic particles, algae, and bacteria) ... basic environment provides conditions ideally suited to bacteria that metabolise cellulose ... Insects cannot metabolise cellulose independently, but the presence of these bacteria allow cellulose to be metabolised into basic sugars ...
Issues With Poultry Farming - Antibiotics
... The mechanism is apparently the adjustment of intestinal flora, favoring "good" bacteria while suppressing "bad" bacteria that provoke inflammation of ... However, this may present the risk of slaughtered chickens harboring pathogenic bacteria and passing them on to humans that consume them ...
Desulfotomaculum
... Desulfotomaculum is a genus of Gram-positive, obligately anaerobic soil bacteria ... A type of sulfate-reducing bacteria, Desulfotomaculum can cause food spoilage in poorly processed canned foods ... They are endospore-forming bacteria ...

Famous quotes containing the word bacteria:

    To the eyes of a god, mankind must appear as a species of bacteria which multiply and become progressively virulent whenever they find themselves in a congenial culture, and whose activity diminishes until they disappear completely as soon as proper measures are taken to sterilise them.
    Aleister Crowley (1875–1947)