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The microbial world is extremely diverse. It includes
algae, archaea, bacteria, fungi, helminths, protists, and viruses.
Algae, fungi, helminths, and protists are eukaryotic. The archaea
and bacteria are prokaryotic. Because the number of bacteria is much
greater than the number of eukaryotic microbes, microbiology has come to
be thought of as primarily bacteriology. Viruses are also quite numerous.
However, viruses are acellular and therefore, technically speaking, not
organisms. BIOL 305 will concentrate on the prokaryotes and viruses.
The other microbes are covered in other courses, including BIOL 303 and
304.
Some History
The microbial world of "little animicules" was first described in the 17th century by Antonie von Leeuwoenhoek. However, the science of microbiology dates to the mid 19th century when technological limitations to the rational study of microbes began to be overcome.
Microbiology has its disciplinary roots in agriculture, chemistry, and medicine. French chemist, Louis Pasteur, first recognized fermentation as a microbial process, rather than merely a chemical change that occured as grape juice aged. This recognition resulted in his development of a heat treatment that prevented wine from becoming sour. This process killed lactic acid producing bacteria that sometimes contaminated wine.
Such "wine diseases" caused serious economic losses. Pasteur theorized that since germs caused diseases of wine they might also be the cause of animal diseases. Nevertheless it was a German physician, Robert Koch, who developed the basic microbiological techniques that led to an experimental protocol to determine the microbial etiology of disease.
Very few microbes actually cause disease. In fact,
microbes are absolutely essential for life to continue on earth.
The basic ecological role of microbes was first suggested by a Dutch professor,
Martinus Beijerinck, who realized that microbes were responsible for maintaining
soil fertility. It was Beijerinck who eventually recognized the underlying
biochemical unity of life.
Microorganisms are Everywhere (the environment selects)
Microorgansisms are small and easily disseminated and
widely distributed. Although microbes are extremely adaptable
as a group, each species has limitations and will only grow and reproduce
where conditions permit. In other words, microorganisms
are everywhere; the environment selects.
In fact, one half of the earth's biomass is estimated to consist of microorganisms.
By comparison, Plants=35%, Animals=15%.
Microbial Habitats/Ecosystems
soil: most numerous in the rhizosphere, also 1 mile down;
water: fresh, brackish, marine, hypersaline;
in and on plants, animals, and even other microorganisms.
The human body contains about 1013 human cells. There are 1014
bacterial cells on human body surfaces. This normal
flora, is
absolutely essential for health. The normal flora are not pathogens.
The Essential Roles of Microorganisms
Microorganisms often live in close association with other organisms. Symbiotic relationships, such as exist between the normal flora and humans, can be beneficial. They can also be harmful as is the case with disease- causing microbes (pathogens). Most microorganisms, however, are free-living.
Microbes are, above all, biogeochemical
agents. In ecological terms
they are decomposers.
Their vital purpose is the decomposition of dead matter so that
its content can be recycled. Decomposers work at the bottom
of a food chain of an ecosystem. The organisms at the top of most
food chains provide the source of nutrients and energy for all of the other
members of the chain.
They are producers. The most common producers are
photosynthetic.
In most cases, energy and nutrients enter an ecosystem by photosynthesis. Producers harvest light energy to assimilate carbon dioxide, water and minerals and synthesize organic molecules. Organic molecules are the food of consumers. Dead producers and consumers are decomposed by fungi and prokaryotic microbes. Decomposition of dead bodies regenerates the raw material for photosyntheis. Thus:
PRODUCERS---->CONSUMERS---->DECOMPOSERS
Marine and fresh water algae and other photosynthetic microbes are the primary producers on earth. In aquatic ecosystems, the cyanobacteria and other photosynthetic prokaryotes are of secondary importance as producers, they are nevertheless essential because of their unique abilities. Aquatic consumers, from protozoa to large animals, feed on the photosynthtic microbes or on those who have consumed photosynthetic organisms.
Microbial photosynthesis is of minor significance on land
where plants hold sway as producers. On land, course, animals are
the main consumers of the large photosynthesizers. The primary role
of microbes on land is decomposition. The importance of microbial
decomposition can be seen if you consider that cellulose is
the most abundant organic material on earth. Hemicelluloses are next. These
can be digested only by microorganisms.
Applied Microbiology (taking advantage of microbial activities)
Microbial decomposition makes sewage disposal plants possible.
Microorganisms are important in food production. Fermentation is the source of foods and and beverages. Some microorganisms are themselves fit to eat.
Spoilage is unwanted decomposition of substances human's value.
Biodegradation and bioremediation involves on-site use of microbial activities to combat pollution.
Chemical and pharmaceutical industries rely on microbes as a source of products.
Biotechnology/genetic engineering depends on genetic resources
of microorganisms..
Microbes to Know
Microorganisms occupy all three domains (superkingdoms) into which living organisms are now classified. See text Figure 10.2.
Eukaryotic microorganisms are classified into kingdoms
of the Domain Eucarya. The green algae are members of the Plant Kingdom.
The yellow algae, brown algae, dinoflagellates, diatoms, protozoa, and
slime molds are found in the Kingdom Protista, while the fungi have a kingdom
of their own.
There are two domains for the prokaryotic microorganisms.
The Domain Eubacteria includes of the cyanobacteria, the green and purple
photosynthetic bacteria, the mycoplasmas, and the Gram positive and Gram
negative bacteria. The Domain Archaea includes the methanogens, extreme
halophiles, and extreme thermoacidophiles.
Viruses, being acellular parasites of cells, are not classified
into any domain or kingdom.the cellular organisms.
Of all the groups of microorganisms, the eubacteria are the best understood. Eubacteria are commonly referred to, simply, as bacteria. Among the eubacteria the Gram positive and Gram negatives have been most studied. These bacteria are identified by their reaction to the Gram Stain and cell wall structure.
Most G- bacteria are rod-shaped, some are spirals. Most
cocci are G+. Other G+ bacteria may be rods. Some G+ bacteria lose
their characteristic staining property characteristic upon aging, becoming
G-.
Some important groups of Gram negative bacteria:
COLIFORMS: rods; fermentative;
mainly gut inhabitants (enterics), associated with fecal pollution; some
free living in soil and water; includes Escherichia
coli, Enterobacter, Salmonella, Shigella, Serratia, Proteus.
PSEUDOMONADS: free living
soil and water rods; nonfermentative; includes Pseudomonas,
Aeromonas.
GREEN SULFUR, PURPLE SULFUR PHOTOSYNTHETIC
BACTERIA:
mainly aquatic; rods, cocci, spirals; anoxygenic, require
H2S; includes Chlorobium, Chromatium.
CYANOBACTERIA: morphologically
diverse, oxygenic
Anabaena, Nostoc
Some important groups of Gram positive bacteria:
LACTIC ACID BACTERIA: rods
or single, pairs, chains of cocci; fermentative; found on plants and in
animals, dairy products; includes Streptococcus,
Enterococcus, Lactobacillus.
SPORE-FORMERS: rods; free
living in soil and water; fermentative; includes Bacillus
(aerobic), Clostridium (anaerobic).
Clostridia cause tetanus, botulism, gas gangrene
MICROCOCCI: cocci in pairs
or clusters; normal flora of animals; includes Micrococcus,
Staphylococcus
CORYNEFORMS: spindle shaped,
X,Y,Z forms, fermenters, normal flora
Corynebacterium, Propionibacterium
MYCOBACTERIA: rods, pseudomycelia,
primitive branching, acid-fast
Mycobacterium, Nocardia
ACTINOMYCETES: filamentous,
mold-like, reproduce by conidia
Streptomyces (give
soil its characteristic, after a rain smell)