The Impact of Microbes on the Environment and Human Activities (page 2)
(This chapter has 4 pages)
© Kenneth Todar, PhD
Associations
with Animals and Plants
Microbes invariably enter into beneficial, sometimes essential,
associations with all higher forms of organisms, including insects,
invertebrates, fish, animals and plants. For example, bacteria and
other microbes in the intestines of animals and insects digest
nutrients and produce vitamins and growth factors. In the plant world,
leguminous plants (peas, beans, clover, alfalfa, etc.) live in intimate
associations with bacteria that extract nitrogen from the atmosphere
and supply it to the plant for growth.
Microbes
in the rumen (forestomach) of cows, sheep and other ruminant animals
are responsible for the initial digestion of nutrients (primarily
cellulose), and they provide not only a source of carbon for their
host, but also a source of protein and vitamins.
The mutualistic association between
nitrogen fixing bacteria and leguminous plants. Left. Nitrogen-fixing Rhizobium bacteria colonized on the
root hairs of clover plants. Right. Nodules containing Rhizobium bacteria on the plant
roots. In the nodule, the bacteria fix nitrogen which they share with
the plant. In exchange, the plant supplies the bacteria with a source
of carbon and energy for growth.
The microbes that normally live in associations with humans on the
various surfaces of the body (called the normal flora), such as Lactobacillus and Bifidobacterium, are known to
protect their hosts from infections, and otherwise promote nutrition
and health.
Lactobacillus
acidophilus and a
vaginal squamous epithelial cell. CDC. L.
acidophilus (informally
known as Doderlein's bacillus) colonizes the vagina during
child-bearing years. As a lactic acid bacterium, the organism creates a
low pH (acidic environment) on the tissues which prevents colonization
by potentially harmful yeast and other bacteria.
Production of
Foods and Fuels
In the home and in industry, microbes are used in the production of
fermented foods. Yeasts are used in the manufacture of beer and wine
and for the leavening of breads, while lactic acid bacteria are used to
make yogurt, cheese, sour cream, buttermilk and other fermented milk
products. Vinegars are produced by bacterial acetic acid fermentation.
Other fermented
foods include soy sauce, sauerkraut, dill pickles, olives, salami,
cocoa and black teas. Yeast are also involved in fermentations to
convert corn and other vegetable carbohydrates into ethanol to make
beer, wine
or gasohol, but bacteria are the agents of most other food
fermentations.
A
variety of fermented foods and beverages produced by microorganisms.
Medical,
Pharmaceutical and Biotechnological Applications
In human and veterinary medicine, for the treatment and
prevention of infectious diseases, microbes are a source of antibiotics
and vaccines.
Antibiotics are substances
produced by microorganisms that kill
or inhibit other microbes which are used in the treatment of infectious
disease. Antibiotics are produced in nature by molds such as
Penicillium and bacteria such
as Streptomyces and Bacillus.
Vaccines are substances derived
from microorganisms used to immunize
against disease. The microbes that are the cause of infectious disease
are usually the ultimate source of vaccines. Thus, a version of the
diphtheria toxin (called toxoid) is used to immunize against
diphtheria, and parts of Bordetella
pertussis cells are used to vaccinate
against pertussis (whooping cough). The use of vaccines such as
smallpox, polio, diphtheria, tetanus and whooping cough has led to
virtual elimination of these diseases in regions of the world where the
vaccines have been deployed.
Some
antibiotics used in veterinary medicine.
Biotechnology
Microbiology makes an important contribution to biotechnology, an area
of science that applies microbial genetics to biological processes for
the production of useful substances. Microorganisms play a central role
in recombinant DNA technology and genetic engineering. Important tools
of biotechnology are microbial cells, microbial genes and microbial
enzymes.
The genetic information for many biological products and biological
processes can be introduced into microbes in order to genetically
engineer them to produce a substance or conduct a process. The genes
can come from any biological source: human, animal, plant or microbial.
This opens the possibility for microbial production of foods, fuels,
enzymes, hormones, diagnostic agents, medicines, antibiotics, vaccines,
antibodies, natural insecticides and fertilizers, and all sorts of
substances useful in our civilization and society. Also, the microbial
genes that encode for these substances, most of which are unknown, are
a tremendous resource of information for application in medicine,
pharmacy, agriculture, food science and biotechnology.
Human
insulin for treatment of diabetes.
Streptokinase
for
dissolving blood clots. Made by recombinant DNA technology. Other
medical products include hormones, vitamins, vaccines, antigens,
antibodies, cytokines, antibiotics and diagnostic agents.
Basic research
Microorganisms, in particular the bacterium, Escherichia coli and the yeast, Saccharomyces, have been used as
model organisms for basic research and the study of cellular life.
Hundreds of thousands of scientific papers have been published on these
two organisms. Because of cell theory and the unity of biological
processes in all organisms, this information provides us with insight
and understanding of life at all levels, including human.
The
famous Meselson and Stahl experiment which proved that DNA replication
is semiconservative was performed with E. coli DNA.
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