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Microbiology
Microbiology is the study
of microorganisms, including unicellular (single-celled) eukaryotes and
prokaryotes, fungi, and viruseses. Today, most of the work in
microbiology is done using methods from biochemistry and genetics. It
is also related to pathology, as many microorganisms are pathogens.
Microbiologists have made many fundamental contributions to biology,
especially in the fields of biochemistry, genetics, and cell biology.
Microbes have many traits that make them ideal model organisms:
- They are small, therefore they do not
consume many resources
- Some have very short generation times
(~30 minutes for E. coli)
- Cells can easily survive in isolation
from other cells
- They can reproduce by mitotic division,
allowing for the propagation of genetically identical (clonal)
populations.
- They
may be frozen for long periods of time. Even if 90% of the cells are
killed by the freezing process, there are millions of cells in a
milliliter of liquid culture.
These traits allowed Joshua and Esther Lederberg to devise an elegant
experiment in 1951 demonstrating that adaptive mutations arise from
preadaptation rather than directed mutation. For this purpose, they
invented replica plating, which allowed them to transfer numerous
bacterial colonies from their specific locations on one agar-filled
petri dish to analogous locations on several other petri dishes. After
replicating a plate of E. coli, they exposed each of the new plates to
phage. They observed that phage-resistant colonies were present at
analogous locations on each of the plates, allowing them to conclude
that the phage resistance trait had existed in the original colony,
which had never been exposed to phage, instead of arising after the
bacteria had been exposed to the virus.
The extensive characterization of microbes has allowed them to be used
as tools in other branches of biology:
- Bacteria (especially E. coli) may be used
to replicate DNA in the form of a plasmid. This DNA is often chemically
modified in vitro then inserted into bacteria to select for the desired
traits and isolate the desired product from by-products of the
reaction. After growing the bacteria and thereby replicating the DNA,
the DNA may be further modified and inserted into other organisms.
- Bacteria may be used to produce large
amounts of protein using genes encoded on a plasmid
- Bacterial genes have been inserted into
other organisms as reporter genes.
- The
yeast two-hybrid system combines bacterial genes with genes from the
organism being studied and inserts them into yeast cells to study
protein-protein interactions within a cellular environment.
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Did You Know?
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Bacteria
(especially E. coli) may be used to replicate DNA in the form of a
plasmid. This DNA is often chemically modified in vitro then inserted
into bacteria to select for the desired traits and isolate the desired
product from by-products of the reaction. After growing the bacteria
and thereby replicating the DNA, the DNA may be further modified and
inserted into other organisms. More...
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Bacteria
grow best in
the temperature range between 4ºC and 60ºC. Temperature below
4ºC, and temperature between 60ºC and 74ºC, will not
kill bacteria, but it will not allow them to multiply enough times to
cause an illness. In order to kill pathogenic bacteria you need
temperatures above 74ºC. Temperature is the easiest factor to
control in order to prevent bacterial growth.
Find
out more...
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Bacterial
intoxication will typically have shorter incubation period than
infection (with sudden onset), which usually only lasts one day and
fever is rarely present. More...
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Improperly
handled
food and equipment, poorly washed dishes and multi-service articles
have potential to spread pathogenic bacteria and open the door for
dangerous foodborne diseases. More...
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