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Bacteria
The bacteria (bacteria) are unicellular organisms prokaryotes (characterized by a lack of nucleus and organelles). Most bacteria have a cell wall carbohydrate, the peptidoglycan. Bacteria measure few micrometers long and may have different forms: spherical forms (shells), elongated shapes or sticks (bacilli), a more or less spiral. The study of bacteria is bacteriology, a branch of microbiology.
The bacteria are ubiquitous and are present in all types of habitats found on Earth. They can be isolated from land, freshwater, brackish or sea, air, ocean depths, radioactive waste, the crust on the skin and the intestines of animals. There are forty million bacterial cells in a gram of soil and one million bacterial cells in a milliliter of water. In all, there are five quintillions (5 × 1030) of bacteria in the world, representing a large part of the biomass of the world. However, many of these bacteria are not yet characterized as non-cultivable laboratory. Bacteria have considerable importance in biogeochemical cycles as the cycle of carbon and nitrogen fixation from the atmosphere.
In humans, it was calculated that 1012 bacteria colonizing the skin, 1010 bacteria colonize the mouth and 1014 live bacteria in the intestine, making it ten times more bacterial cells than human cells in the body Human. Most of these bacteria are harmless or beneficial to the body. However, there are many species of pathogens responsible for many infectious diseases such as cholera, syphilis, plague, anthrax, tuberculosis. Most often fatal bacterial diseases are respiratory infections, tuberculosis alone kills about 2 million people each year, mainly in sub-Saharan Africa. Bacteria can cause respiratory or intestinal disorders while others may be responsible for the infection of injury. Bacterial infections can be treated with antibiotics that most often inhibit one of their vital function (eg penicillin blocking the synthesis of the cell wall).
Bacteria can be very useful to humans in the process of sewage treatment in the food industry in the manufacture of yoghurt or cheese and industrial production of many chemicals.
History
The bacteria are microscopic, they are not visible with a microscope. Antony van Leeuwenhoek was the first to observe bacteria through a microscope of its production in 1668. He called "Pet" and published his observation in a series of letters he sent to the Royal Society.
The word "bacteria" appears for the first time with the German microbiologist Christian Gottfried Ehrenberg in 1828. The word derives from the Greek βακτηριον, which means "stick".
In the nineteenth century, the work of Louis Pasteur revolutionized bacteriology. It showed in 1859 that the fermentation process is caused by micro-organisms and that this growth was not due to spontaneous generation. It also demonstrates the role of micro-organisms such as infectious agents. Shepherd also conceived of culture, processes of destruction of micro-organisms such as autoclaving and pasteurization.
The German physician Robert Koch and his staff began developing the technology culture of bacteria on solid medium. Robert Koch is one of the pioneers of medical microbiology, he worked on cholera, anthrax (anthrax) and tuberculosis. It clearly showed that bacteria could be the causative agent of infectious disease and he proposed a series of assumptions (the Koch's postulates, still used today) confirming the etiologic role of a micro organism in a disease. He won the Nobel Prize for medicine and physiology in 1905.
Although we knew in the nineteenth century that bacteria are the cause of many diseases, there was no antiseptic available. In 1910, Paul Ehrlich developed the first antibiotic, by changing colors selective tinted Treponema pallidum it spirochaete that causes syphilis-compounds that kill the pathogen of selectively. Ehrlich received in 1908 the Nobelpour taken this work on immunology, and pioneered the use of dye to detect and identify bacteria, his work is the basis of Gram staining and staining Ziehl-Neelsen.
Microbiologists Martinus Beijerinck and Sergei Winogradsky initiated the first work of environmental microbiology and microbial ecology by studying microbial communities of soil and water and relations between these micro-organisms.
If the bacteria were known in the nineteenth century, there were still no antibacterial treatment. In 1909, Paul Ehrlich set to develop a treatment against syphilis before the use of penicillin in therapy suggested by Ernest Duchesne in 1897 and studied by Alexander Fleming in 1929.
In 1977, Carl Woese through its work in molecular phylogeny prokaryotes divided into two groups: Bacteria and Archaea.
Cell Structure
As prokaryotic (non core), bacteria cells are relatively simple, characterized by a lack of nucleus and organelles such as mitochondria and chloroplasts, they do not have an endoplasmic reticulum or device golgi.
An important feature is the bacteria cell wall. Bacteria can be divided into two groups (Gram positive and Gram negative) based on the difference in the structure and chemical composition of the cell wall underscored by the Gram staining. The bacteria stain Gram positive have a cell wall containing peptidoglycan (or murein) thick and acids while teichoiques bacteria stain Gram negative peptidoglycan end are located in the periplasm between the cytoplasmic membrane and outer membrane. The wall gives the bacterium its shape and protects against the outbreak as a result of the very high osmotic pressure of the cytoplasm. The peptidoglycan provides rigidity of the wall. However, there are bacteria without walls: the mycoplasma.
Intracellular
The bacteria were seen as mere bags cytoplasm, but many levels of structural complexity have been found since the discovery of prokaryotic cytoskeleton, and location of specific proteins in the bacterial cytoplasm. These subcellular compartments were named bacterial hyperstructure "(" bacterial hyperstructures "in English).
Bacteria have a form of chromosome DNA filament in support of heredity. The bacterial chromosome is generally circular. In addition to this genomic DNA, cells often contain bacterial DNA molecules extra-chromosomal circular called plasmids. The cells also contain many ribosomes for protein synthesis through the mechanism of translation. The cytoplasm of prokaryotes often contains substances intracellular reserve stocks which are nutrients in the form of glycogen, starch or poly-b-hydroxybutyrate (PBH). Some species of aquatic bacteria have gas vesicles that provide buoyancy cells. Other species, bacteria magnetotactiques have the particularity to present a magnetosome.
Extracellular
Many bacteria have extra-cellular structures such as flagella used for the mobility of cells, and fimbriae allowing the attachment or the phenomenon of conjugation. Heterotrophic bacteria can use their flagella to move to areas rich in organic substances (nutrients) thanks to the phenomenon known as chemotaxis.
Some bacteria can produce thin layers outside the cell wall, usually consisting of polysaccharides (sugars). When the layer is compact, we talk about capsule. The capsules are such a barrier protecting the cell against the external environment and also against phagocytosis. It also facilitates attachment to surfaces and the formation of biofilms. Klebsiella, Bacillus anthracis, Streptococcus pneumoniae are examples of bacteria capsuleas. When the layer is diffuse, there is talk of mucoid layer. When the layer is thicker, we talk about glycocalyx. The glycocalyx allows bacteria to adhere to a substrate.
Some bacteria called engaineas bacteria produce a dense outer layer and rigid: the sheath. This phenomenon is common in bacteria of the water channels that form filamentous (Sphaerotilus natans for example). The jacket protects cells against the turbulence of the water. The bacteria Cytophaga group - Flavobacterium produce a mucous layer that allows them to remain in close contact with a solid. Other bacteria such as Spirillum can be wrapped with a layer called the protein layer S.
Mutual
In soil, bacteria in the rhizosphere (soil attached to the roots of plants) fix nitrogen and produce nitrogen compounds used by plants (such as bacteria or Azotobacter Frankia). In exchange, excrete the plant roots level of sugars, amino acids and vitamins that stimulate the growth of bacteria. Other bacteria such as Rhizobium are associated with leguminous plants at nodules on the roots.
There are many symbiotic relationships or mutual bacteria with invertebrates. For example, animals that thrive near hydrothermal vents on the ocean floor as Riftia Pachyptila tubeworms, mussels or shrimp Bathymodiolus Rimicaris exoculata live in symbiosis with bacteria-chimiolitho autotrophic.
Buchnera is a bacterium endosymbiotic aphids (aphid). She lives inside the cells of the insect and providing essential amino acids. The bacterium Wolbachia is housed in the testes or ovaries of certain insects. This bacterium can control the reproductive capabilities of its host.
Bacteria are associated with termites and to provide sources of nitrogen and carbon.
Bacteria colonizing the rumen herbivores allow the digestion of cellulose by these animals. The presence of bacteria in the intestines of humans helps to digest food but also bacteria produce vitamins as pholique acid, vitamin K and biotin.
Bacteria colonize the crop of a bird folivore (consumer leaves), the Hoazin (Opisthocomus hoazin). These bacteria help to digest the cellulose sheets in the same manner as in the rumen of ruminants.
Bioluminescent bacteria as Photobacterium are often associated with fish and marine invertebrates. These bacteria are housed in specific organs at their hosts and emit light through trees: the luciferase. This luminescence is used by the animal at various behavior such as reproduction, the attraction of prey or deter predators.
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