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a)  Production of food: cheese, yogurt, vinegar, wine, sour cream, etc.
b)  Industry : cleaning up petroleum, remove waste products from the water,
    synthesize drugs and chemicals.
Symbiosis : The interdependence of different species, which are
sometimes called symbionts. There are three main types of symbiosis,
based upon the specific relationship between the species involved:
mutualism, parasitism, and commensalism.  Symbiosis that results in
mutual benefit to the interdependent organisms is commonly known as
mutualism. An example of mutualism is the coexistence of certain
species of algae and fungi that together compose lichens. Their close
association enables them to live in extreme environments, nourished
only by light, air, and minerals. Living separately, the alga and
fungus would not survive in such conditions.  In parasitism, also known
as antagonistic symbiosis, one organism receives no benefits and is
often injured while supplying nutrients or shelter for the other
organism. Parasites include viruses and bacteria that cause many
diseases; certain protozoans that can infect plants and animals;
tapeworms and flukes that infest the intestinal tracks and internal
organs of animals.  The type of symbiosis known as commensalism is a
food-sharing association between two different kinds of nonparasitic
animals, called commensals, that is harmless to both and in many cases
is mutually advantageous. Many commensals are free to separate. Other
commensals function together so completely that they cannot separate.
They do not harm each other. An example is a polyp found in deep water
off the coast of Newfoundland. It attaches itself to the shell of a
certain species of hermit crab and, by budding, covers the entire shell
with a colony that dissolves the original shell. Because the colony
grows at the same rate as the crab, it furnishes continuous protection,
and the crab does not shed its shell at periodic intervals as it
normally would. The polyp, in turn, benefits by moving about with the
crab, thereby obtaining a greater food supply than it would if attached
to a stationary object.
Uses of Bacteria in the Environment :
Bacteria feed on dying material and convert it back into basic
substances. This process of decomposition is as significant as
photosynthesis, for without it food chains would cease, and fallen
trees, leaves, and other refuse would simply pile up. Bacteria also
strongly influence the movement of key elements, such as sulfur, iron,
phosphorus, and carbon, around the globe. The weathering of rocks,
which releases elements back into life systems for use, is
substantially enhanced by the breakdown processes of bacteria.
Uses of Bacteria in Sewage Disposal :  The main cleansing agents in
sewage treatment are a variety of specialized bacteria that convert,
mostly through fermentation, the organic materials of sewage into
carbon dioxide, methane, and hydrogen gases. There is a bacterial
species involved with the production of nearly every familiar product.
For example, vinegar, which is used as both a flavor enhancer and an
important food preservative, results from the conversion of ethyl
alcohol to acetic acid by acetic-acid bacteria. Specific enzymes
extracted from bacteria are used in spot removers, meat tenderizers,
laundry starches, and household detergents. Bacteria are now used
throughout the growing biotechnology industry in the development of new
products for medical treatment. Bacteria that can digest petroleum are
even used in oil-spill cleanups.
Nitrogen Fixation :  Biological or industrial process by which
molecular atmospheric nitrogen is converted into a chemical compound
that is essential for plant growth and is also used in industrial
chemical production.
The most widely used and most productive of the soil microorganisms
capable of nitrogen fixation are symbiotic bacteria of the genus
Rhizobium, which colonize and form nodules on the roots of leguminous
plants such as clover, alfalfa, and peas. These bacteria obtain food
from the legume, which in turn is supplied with abundant nitrogen
compounds. Soils are sometimes inoculated with a particular species of
Rhizobium to increase a legume crop, which is often planted to
replenish the nitrogen depleted by other crops.
Much smaller amounts of nitrogen are fixed in the soil by nonsymbiotic (free-living) bacteria such as the aerobes, which function in the presence of oxygen, and bacteria of the genera Klebsiella and Bacillus, which function without oxygen. Some forms of cyanobacteria (formerly known as blue-green algae) also fix nitrogen, such as the alga Anabaena, which, in symbiosis with the water fern Azolla pinnata, is said to markedly increase rice yields, as was the case in paddies in the Th‡i B“nh region of northern Vietnam. The need for fixed nitrogen in agriculture today is far greater than can be supplied by natural biological processes, and the production of nitrogen compounds from atmospheric nitrogen is a major chemical industry.
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