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Microorganisms are the foundation of the biosphere. Without them other life forms would not have evolved and could not exist. Microorganisms established the geochemical conditions on earth that enabled evolution of plants and animals. Plants and animals are descended from microorganisms and their cells are now known to be composites of microorganisms. For example the mitochondria of all plants and animals are derived from bacteria. Similarly, the photosynthetic organelle the chloroplast, found in all plants and algae are descended from a group of photosynthetic bacteria, the cyanobacteria. Cyanobacteria are believed to be the first organisms on earth to produce the free oxygen gas and concomitantly, the protecting ozone layer around earth, thereby providing condition for evolution of land plants and animals.
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Humans and other animals, as well as plants are completely dependent on microorganisms for life. Like all animals, humans harbor billions of microorganisms in their digestive tracts, microorganisms necessary to digest food and provide nutrients for growth and a source of energy. Plants also require microorganisms to provide nutrients for growth an activity that takes place largely in root systems. There the organic materials such as nitrogen and phosphorus , the natural fertilizers made available by microorganisms and required by plants for growth and development. Microorganisms exist everywhere physical conditions permit. Although lake water may appear transparent to the eye, a liter of the water can harbor a billion bacteria. A gram of soil can also contain over a billion bacteria. Many microorganisms have special dispersal cells that can be carried by wind across and between continents. In addition, birds and insects transport microorganisms as they fly. Thus, we live in a world teeming with microbial life that carries out a myriad of activities essential for sustaining the biosphere of earth.
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Microorganisms are highly diverse genetically and metabolically, for more so than plants and animals. This should not seem surprising because microorganisms have existed on earth for over 3.5 billion years. From analysis of molecular sequences of genes such as 16s and 18s ribosomal RNA, approximately 20 separate main phylogenetic groups of microbial life have been identified, comparable in depth and breadth to the animal and plant kingdoms.
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One of the most surprising characteristics of microorganisms in range of physiological conditions under which they flourish they grow across broad ranges of temperatures, pH, salt concentration and oxygen concentration. Some thrives at boiling temperature in hot spring and at temperatures higher than 1000 C in submarine vents. Other are found in sea ice off Antarctica and at the North pole. Some produce sulphuric and nitric acids, and many microbial species live without oxygen. Other live in saturated salt brines and some are resistant to high levels of radioactivity.
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The variety of metabolic types of microorganisms is enormous. Some are photosynthetic and like plants produce oxygen in this process. In fact this “biotechnology” first occurred in the cyanobacteria, which subsequently evolved endosymbiotically to form chloroplasts that enable algae and plants to conduct photosynthesis. Other bacterial groups carry out photosynthesis by different pathways and produce products such as sulfur. Microorganisms are the primary, if not sole agents responsible for degradation of a great variety of organic compounds including cellulose, hemicellulose, lignin, and chitin (the most abundant organic matter on earth). If it were not for microbial activities involved in natural decay, excessive amounts of organic matter would accumulate in forests and aquatic sediments. In addition microorganisms are responsible for degradation of toxic chemicals derived from anthropogenic sources, such as PCBs (polychlorinated biphenyls), Dioxins and other pesticides, Because microorganisms are so versatile , they are relied upon to digest water in sewage treatment plants, landfills, and toxic waste sites. It is in this regard that the field of bioremediation, encompassing all of the processes is still in its infancy. Much needs to be learned before microbial breakdown processes can be controlled and enhanced in situ.
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Microorganisms play important roles in geochemical processes. For example the global nitrogen cycle in nature is dependent on microorganisms unique processes carried out by microorganisms include nitrogen fixation (the natural conversion of atmospheric denitrogen gas to utilizable organic cell nitrogen), oxidation of ammonia and nitrite to nitrate, and nitrate reduction with formation of dinitrogen and nitrous oxide gases. Similar important and unique roles are played in other cycles, such as sulfur and carbon cycles as well as in oxidation and reduction of metals. If it were not for microorganisms, substances such as cellulose and lignin would not be recycled; they would accumulate in the environment. Induced almost all organic substance are recycled via activities of bacteria, fungi and protozoa.
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The importance of microorganisms in agriculture is enormous and extends beyond geochemical cycles. Indeed, most of the fertility of soil derived from microbial mineralization and in production of nitrogen for plant growth. These processes extended to lichen and cyanobacteria dominated soils which occupy a larger surface area on earth than in tropical rain forests. Mycorrhizal fungi form important rhizosphere associations with almost all plants. Such associations are essential for optimum growth and in fact permit some plants to grow in areas they could not otherwise colonize. Recent advances in agriculture stem from breakthroughs in the genetic engineering of plants; one of the most dramatic examples is that of the bacterium.
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Agrobacterium tumefaciensnormally the curative of crown gall disease in plants, this bacterium has been used to transfer favorable properties into an agriculturally important plant species there by providing a mechanisms for introducing genes that provide resistance to plant diseases, insect or pesticides into plants. Microorganisms are important in recycling waste materials. Sewage (waste water) treatment and the breakdown of garbage in landfills occur because of microorganisms. These microorganisms do this “for free” because in most cases they derive energy from the process.
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A recent discovery indicates that microorganisms may influence weather. Some marine algae produce dimethyl sulphide (DMS). This compound is volatile and escapes into the atmosphere where it is photooxidized to form sulfate. The sulfate acts as a water nucleating agent and when enough sulfate is formed, clouds are produced; these clouds have three major impacts. First they shade the ocean and, thereby, slow further algal growth and DMS production, eventually decreasing cloud formation. Second the clouds lead to increased rainfall. And third, because clouds are reflective of incoming sunlight, the clouds reduce the amount of heat that reaches earth moderating global warming.
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Microorganisms are at the core of biotechnology. Many antibiotics and antitumor agents are derived from microorganisms including penicillin, streptomycin and chloramphenicol. The emergence of multiple antibiotic resistant pathogenic bacteria has necessitated the search for new antibiotics. Because there are so many types of microorganisms they produce many unique products currently useful in biotechnology and offer great promise for exploitation in the future.
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