Dictionary
(microbiology) single-celled or noncellular spherical or spiral or rod-shaped organisms lacking chlorophyll that reproduce by fission important as pathogens and for biochemical properties taxonomy is difficult often considered to be plants
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Wikipedia
lightgrey name = Bacteria caption = ''Escherichia coli'' lightgrey Bacteria Taxobox_end_placement lightgrey plural_taxon = Phylum (biology)Phyla/Division (biology)Divisions Actinobacteria
Aquificae
Bacteroidetes/Chlorobi< ;br? !/>Chlamydiae/Verrucomicrobi aChloroflexi
Chrysiogenetes
Cyanobacteria
DeferribacteraceaeDeferribacteres
Deinococcus-Thermus
Dictyoglomi
Fibrobacteres/Acidobacter iaFirmicutes
Fusobacteria
Gemmatimonadetes
Nitrospirae
Planctomycetes
Proteobacteria
Spirochaetes
Thermodesulfobacteria< br? />Thermomicrobia
ThermotogaeTaxobox_end Bacteria (singular, bacterium) are a major group of living organisms. Most are microscopic and unicellular, with a relatively simple cell structure lacking a cell nucleus, and organelles such as mitochondrionmitochondria and chloroplasts. Their cell structure is further described in the article about prokaryotes, because bacteria are prokaryotes, in contrast to organisms with more complex cells, called eukaryotes. The term "bacteria" has variously applied to all prokaryotes or to a major group of them, otherwise called the eubacteria, depending on ideas about their relationships. In Wikipedia, bacteria is used specifically to refer to the eubacteria.Bacteria are the most abundant of all organisms. They are ubiquitous in soil, water, and as symbiosissymbionts of other organisms. Many pathogens are bacteria. Most are minute, usually only 1 E-6 m0.5-5.0 μm in their longest dimension, although giant bacteria like ''Thiomargarita namibiensis'' and ''Epulopiscium fishelsoni'' may grow past 0.5 mm in size. They generally have cell walls, like plant and fungusfungal Cell (biology)cells, but with a very different composition (peptidoglycans). Many move around using flagellumflagella, which are different in structure from the flagella of other groups.
History and taxonomy - The first bacteria were observed by Antony van Leeuwenhoek in 1683 using a single-lens microscope of his own design. The name ''bacterium'' was introduced much later, by Christian Gottfried EhrenbergEhrenberg in 1828, derived from the Greek word !βακτη ριον? meaning "small stick". Louis Pasteur (1822-1895) and Robert Koch (1843-1910) described the role of bacteria as conveyors and causes of disease or pathogens.
Reproduction - Bacteria reproductionreproduce only asexual reproductionasexually, not genetic recombinationsexually. Specifically they reproduce by binary fission, or simple cell division. During this process, one cell divides into two daughter cells with the development of a transverse cell wall.
Metabolism - Bacteria show a wide variety of different metabolisms and can accordingly be classified into primary nutritional groups. The most common division is between heterotrophs, which depend on an organic source of carbon, and autotrophs, which are able to synthesize organic compounds from carbon dioxide and water. Autotrophs that obtain energy by oxidizing chemical compounds are called chemotrophs, and those that obtain their energy from light, via photosynthesis, are called phototrophs. There are many variations on this terminology such as chemoautotrophs and photosynthetic autotrophs and so on. In addition, bacteria are distinguished based on the source of reducing equivalents they are using. Those using inorganic compounds (e. g. water, hydrogen, sulfide or ammonia) for this purpose are called lithotrophs and others needing organic compounds (e. g. sugars or organic acids) and are called organotrophs. The metabolic modes of energy metabolism (phototrophy or chemotrophy), reducing equivalent sources (lithotrophy or organotrophy) and carbon sources (autotrophy or heterotrophy) can be combined differently in any single microorganism, and even shifting between different modes frequently occurs in many species.Other nutritional requirements include nitrogen, sulfur, phosphorus, vitamins and metallic elements such as sodium, potassium, calcium, magnesium, manganese, iron, zinc, cobalt, copper and nickel for normal growth. For some species, additional trace elements such as selenium, tungsten, vanadium or boron are needed.Based on their response to oxygen, most bacteria can be placed into one of three groups: Some bacteria can grow only in the presence of oxygen and are called aerobes; others can grow only in the absence of oxygen and are called anaerobes; and some can grow in the presence or absence of oxygen and are called facultative anaerobes.
Movement - ''Motile'' bacteria can move about, either using flagellumflagella, bacterial gliding, or changes of buoyancy. A unique group of bacteria, the spirochaetes, have structures similar to flagella, called axial filaments, between two membranes in the periplasmic space. They have a distinctive helixhelical body that twists about as it moves.Bacterial flagella are arranged in many different ways. Bacteria can have a single polar flagellum at one end of a cell, clusters of many flagella at one end or flagella scattered all over the cell, as with ''Peritrichous''. Many bacteria (such as ''E.coli'') have two distinct modes of movement: forward movement (swimming) and tumbling. The tumbling allows them to reorient and introduces an important element of randomness in their forward movement. (see external links below for link to videos).Motile bacteria are attracted or repelled by certain stimulus stimuli, behaviors called ''taxes'' - for instance, chemotaxis, phototaxis, mechanotaxis and ? it.wikipedia.org - magnetotaxis (Italian). In one peculiar group, the myxobacteria, individual bacteria attract to form swarms and may differentiate to form fruiting bodies. The myxobacteria move only when on solid surfaces, unlike ''E. coli'' which is motile in liquid or solid media.
Groups and identification - !image:bacteria_shape.png rightframedBacteria come in a wide variety of shapes:
A. Rod-shaped
B. Round-shaped or spherical.
C. Round-shaped in clusters.
D. Round-shaped in twos.
E. Spiral-shaped.
F. Comma-shaped. Bacteria come in a variety of different shapes. Most are rod-shaped, sphere-shaped, or helix-shaped; these are respectively referred to as bacillusbacilli, coccuscocci, and spirillumspirilla. An additional group, vibrios, are comma-shaped. Shape is no longer considered a defining factor in the classification of bacteria, but many genera are named for their shape (e.g. ''Bacillus'', ''Streptococcus'', ''Staphylococcus'') and it is an important part in their identification.Another important tool is Gram staining, named after Hans Christian Gram who developed the technique. This separates bacteria into two groups, based on the composition of their cell wall. The first formal grouping of bacteria into phyla was based largely on this test: Gracilicutes - bacteria with a second cell membrane containing lipids, giving them Gram-negative stains Firmicutes - bacteria with a single membrane and thick peptidoglycan wall, giving them Gram-positive stains Mollicutes - bacteria with no second membrane or wall, giving them Gram-negative stainsThe archeabacteria were originally included as the Mendosicutes. As given, these phyla are no longer believed to represent monophyletic groups. The Gracilicutes have been divided into many different phyla. Most gram-positive bacteria are placed in the phyla Firmicutes and Actinobacteria, which are closely related. However, the Firmicutes have been redefined to include the mycoplasmas (Mollicutes) and certain Gram-negative bacteria.
Benefits and dangers - Bacteria are both harmful and useful to the natural environmentenvironment, and animals, including humans. The role of bacteria in disease and infection is important. Some bacteria act as pathogens and cause tetanus, typhoid fever, pneumonia, syphilis, cholera, foodborne illness and tuberculosis. Sepsis, a systemic infectious syndrome characterized by shock and massive vasodilation, or localized infection, can be caused by bacteria such as streptococcus, staphylococcus, or many gram-negative bacteria. Some bacterial infections can spread throughout the host's body and become ''systemic''. In plants, bacteria cause leaf spot, fireblight, and wiltingwilts. The mode of infection includes contact, air, food, water, and insect-borne microorganisms. The hosts infected with the pathogens may be treated with antibiotics, which can be classified as bacteriocidebacteriocidal and bacteriostatic, which at concentrations that can be reached in bodily fluids either kill bacteria or hamper their growth, respectively. Antiseptic measures may be taken to prevent infection by bacteria, for example, prior to cutting the skin during surgery or swabbing skin with alcohol when piercing the skin with the needle of a syringe. Sterilization (microbiology)Sterilization of surgical and dental instruments is done to make them ''sterile'' or pathogen-free to prevent contamination and infection by bacteria. ''Sanitizers'' and disinfectants are used to kill bacteria or other pathogens to prevent contamination and risk of infection.In soil, microorganisms help in the transformation of nitrogen to ammonia with enzymes secreted by these microbes, which reside in the rhizosphere (a zone that includes the root surface and the soil that adheres to the root after gentle shaking). Some bacteria are able to use molecular nitrogen as their source of nitrogen, converting it to nitrogenous compounds, a process known as nitrogen fixation. Many other bacteria are found as symbionts Bacteria in the human bodyin humans and other organisms. For example, their presence in the large intestine can help prevent the growth of potentially harmful microbes.The ability of bacteria to degrade a variety of organic compounds is remarkable. Highly specialized groups of microorganisms play important roles in the mineralization of specific classes of organic compounds. For example, the decomposition of cellulose, which is one of the most abundant constituents of plant tissues, is mainly brought about by aerobic bacteria that belong to the genus ''Cytophaga''. This ability has also been utilized by humans in industry, waste processing, and bioremediation. Bacteria capable of digesting the hydrocarbons in petroleum are often used to clean up oil spills. Some beaches in Prince William Sound were fertilized in an attempt to facilitate the growth of such bacteria after the infamous 1989 Exxon Valdez oil spill. These efforts were effective on beaches that were not too thickly covered in oil. Bacteria, often in combination with yeasts and molds, are used in the preparation of fermented foods such as cheese, pickles, soy sauce, sauerkraut, vinegar, wine, and yogurt. Using biotechnology techniques, bacteria can be bioengineered for the production of therapeutic drugs, such as insulin, or for the bioremediation of toxic wastes.
Miscellaneous - Two organelles, mitochondrionmitochondria and chloroplasts, are generally believed to have been derived from endosymbiotic theoryendosymbiotic bacteria.Microorganisms are widely distributed and are most abundant where they have food, moisture, and the right temperature for their multiplication and growth. They can be carried by air currents from one place to another. The human body is home to billions of microorganisms; they can be found on skin surfaces, in the intestinal tract, in the mouth, nose, and other body openings. They are in the air one breathes, the water one drinks, and the food one eats.The great antiquity of the bacteria has enabled them to evolve a great deal of genetic diversity. They are far more diverse than, say, the mammals or insects. For instance, the genetic distance between ''E. coli'' and ''Thermus aquaticus'' is greater than the distance between humans and oak trees.
See also - Bacterial growthBacteriocinMicroorganismNanobacterium
References - Some text in this entry was merged with the ''Nupedia'' article entitled ''Bacteria'', written by Nagina Parmar; reviewed and approved by the Biology group (editor: Gaytha Langlois, lead reviewer: Gaytha Langlois, lead copyeditors: Ruth Ifcher and Jan Hogle) NCBI-scienceprimer
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Websites
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Irish Centre of Integrated Medicine
The Irish Centre of Integrated Medicine ICIM is a prestigious medical practice working with doctors, scientists, reserches and practitioners to identify the patient's root of the complaint using natural medicine and conventional diagnostics to achieve the level of expertise necessary. ICIM believe that a succesfull treatment depends upon a successful diagnosis.
http://www.icim.ie/
University of California Museum of Paleontology
Physically located in Berkeley, California, site contains information about exhibits, outreach, and extensive educational resources and links.
http://www.ucmp.berkeley.edu/
Virtual Museum of Bacteria
The museum provides information for the general public on all aspects of bacteria with integrated hyperlinks to >250 relevant sites. Annotated lists of links are also provided for professional microbiologists
http://www.bacteriamuseum.org
Stalking the Mysterious Microbe
Are microbes just germs? Join microbiologist Sam Sleuth to learn more about microbes like bacteria and viruses. Find out what microbes look like, how they evolved and where bacteria and viruses live.
http://www.microbe.org/
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