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Unit 1 Notes
The Science of Microbiology
“The microbe that felled one child in a distant continent yesterday can reach yours today and
seed a global pandemic tomorrow.”
Joshua Lederberg, Nobel Prize Winner, 1958
What Is Microbiology?
Microbiology is defined as the study of microorganisms, or living things that are too small to be seen by the
naked eye.
Statistics
Did you know that 25% of all deaths worldwide are due to infectious diseases (diseases caused by microbes)?
The majority are respiratory infections, then AIDS, then diarrheal diseases.
Why Do Microbes Matter?
In spite of their tiny size, they have an enormous impact on our lives. Before the development of microbiology
as a science, pathogens (microbes that cause human disease) often controlled human events. Microbes perform
many functions in our lives. Here are some:
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Some cause diseases; some decompose dead organisms
Some control pathogens in soil and maintain nature’s balance
Some capture energy from the sun
Some are used as insecticides and pesticides to control insects
Some are used in the field of genetic engineering
Some are used to make many of our food products, such as yogurt and beer
Some are used to produce products we need such as insulin, medicines, etc.
Some can be used to clean up oil spills and other toxic waste in the environment, called
bioremediation
The First Observations
Bacterial ancestors were the first living cells to appear on Earth. Following are some of the first observations to
be made in the discovery of microorganisms:
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In 1665, an Englishman named Robert Hooke was the first to notice that life's smallest living units
were made up of "cells", which was the beginning of the cell theory (all living things are composed
of cells).
In the late 1674, Dutch scientist Antoni van Leeuwenhoek invented the first true microscope. He is
the first to describe living microbes (he called them "animalcules").
The Debate Over Spontaneous Generation
Until the late 1800's, people believed that life could arise spontaneously from nonliving matter (spontaneous
generation).
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In 1668, Francisco Redi did an experiment that demonstrated that maggots did not arise
spontaneously from meat, and this was the beginning of the disproving of the spontaneous
generation theory.
In 1858, German scientist Rudolf Virchow challenged spontaneous generation with the concept of
biogenesis, which says that living cells can only arise from other living cells.
In 1859, however, Louis Pasteur settled the issue once and for all. In his experiments, he
demonstrated conclusively that microbial life can be destroyed by heat. This was the beginning of
aseptic technique, which is the use of techniques that prevent contamination by unwanted
microorganisms, which is now standard practice in laboratories and medical facilities. He is credited
with development of the "germ theory of disease", which states that germs, or microbes, are the
causative agents of disease.
The Golden Age of Microbiology
The science of microbiology blossomed during a period of about 60 years, and this began in 1857 with
Pasteur’s proposal of the germ theory of disease and continued into the 20th century, up until about World War
I. This period was called the Golden Age of Microbiology. During these years, many branches of
microbiology were established, and these findings led the way to modern microbiology, and many new disease
and disease agents were discovered.
In the 1930’s and 1940’s, the electron microscope was invented, and because a microbe can be multiplied about
100,000 times with these microscopes, viruses (the smallest microorganisms) were then discovered. At about
the same time, antibiotics were discovered. After World War II, more money was available for research, and
microbial genes were beginning to be studied. Here are some important discoveries during this time period:
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In 1796, Edward Jenner was the first to "vaccinate" people against smallpox by inoculating people
with the pus from smallpox victims, thus immunizing them against the virus. This was before
people even knew that microorganisms caused disease! The first real vaccines were made in the
early 1880’s by Pasteur.
In the 1860's, Joseph Lister, an English surgeon, was the first to apply the asceptic technique to
medical procedures. He began treating surgical wounds with a phenol solution, which killed
microorganisms.
In 1876, Robert Koch, a German physician, proved that bacteria actually caused disease. He came
up with a procedure to determine if a specific germ causes a specific disease, called Koch's
postulates.
In the late 1800's, Pasteur discovered fermentation (the process where yeast converts sugars to
alcohol in the absence of air). He also discovered pasteurization (the process of heating food at low
temperatures for a long time to kill bacteria).
Microbiology Today
After the Golden Age of Microbiology, advances in the field of microbiology continued to be made in 4 key
areas: chemotherapy, immunology, virology, and genetic engineering.
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Chemotherapy – chemotherapy is the treatment of disease with chemicals called drugs. Now that
the relationship between microbes and disease had been established, scientists now focused on
finding substances that could cure disease.
o In 1910, Paul Ehrlich, a German physician, created the first drug for the treatment of
syphilis. He is called the father of modern chemotherapy because he was the first to
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come up with the principle of selective toxicity (a successful drug must only kill the
microbe, not the host).
o In 1928, Alexander Fleming, a Scottish physician, discovered the first antibiotic called
"penicillin" from mold. It wasn't until the 1940's that penicillin was finally massproduced.
Immunology – this is the study of the immune system and how to develop vaccines to protect it.
Virology – this is the study of viruses. The first virus was discovered in 1892 by Dmitri Iwanowski,
and it was the tobacco mosaic virus.
Genetic Engineering – this is the process where researchers take the genes from one organism,
manipulate them in the laboratory, and insert them into another organism.
The Microbial World
1. Archaea – discovered in the 1970’s, these are the “ancient” bacteria. They are also called “extremists”
because they survive in extreme conditions. No archaea are human pathogens. They are so different
from normal bacteria that they have their own group. They thrive in conditions that mimic those found
more than 3.5 billion years ago. Lack a true nucleus. Cell walls contain different kinds of amino acids
and sugars than do bacteria, as well as different lipid structures. They are living fossils. They have been
found in acid, in ice, and in salt where normal bacteria cannot grow. Here are the basic types:
a. Thermophiles – love hot temperatures. Can survive over 110 degrees Celsius.
b. Psychrophiles – love cold temperatures. Have been found at -10 degrees Celsius.
c. Halophiles – love salty habitats. Can survive in up to 9% salt water (ocean water is 0.9%).
d. Acidophiles – love acidic conditions.
2. Bacteria – unicellular organisms that are classified according to their shapes; they are found everywhere.
They are found in air, soil, water, on plants and animals, etc. Can be heterotrophic or autotrophic. Most
utilize oxygen, but some operate anaerobically. Can be beneficial or harmful. The most numerous
organisms on the Earth!
3. Viruses – made of a core of nucleic acid with a protein coat, viruses cannot survive on their own. They
need host to metabolize nutrients, produce and excrete wastes, move around, and reproduce. Can infect
all types of cells, including bacterial, fungal, protozoa, plants, animals, and human. They are the
simplest and tiniest of microbes – up to 10,000 times smaller than bacteria. Includes two subgroups:
a. Viroids – like viruses, but contain only RNA with no protein coat.
b. Prions – like viruses, but do not contain nucleic acids. Just made of protein, but can transmit
disease (Mad Cow Disease).
4. Protists – eukaryotic cells that are a very diverse group. The word “protist” comes from the Greek word
meaning “very first”, and this is so because the protists are considered to be the first eukaryotes to appear
on the earth. Classified by whether they are most like plants, animals or fungi. Include amoebas and
algae.
5. Fungi – range in size from single-celled organisms to multi-celled organisms. Major decomposers of
organic matter on Earth. Distinguished from other microbes by their physical appearance and by how
they obtain their food. They secrete enzymes to break down organic matter. Cannot undergo
photosynthesis. Many cause human disease.
6. Helminths – multicellular eukaryotic animals that possess digestive, circulatory, nervous, excretory, and
reproductive systems. Also known as worms, they are parasitic: they must live inside a host in order to
reproduce.
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Characteristic
Bacteria
Protists
Fungi
Helminths
Cell type
Size
Cell Wall
Reproduction
Energy process
Prokaryotic
Microscopic
Present
Binary fission
Heterotrophic
Eukaryotic
Microscopic
Absent
Sexual and asexual
Heterotrophic
Eukaryotic
Macroscopic
Present
Sexual and asexual
Heterotrophic
Eukaryotic
Macroscopic
Absent
Sexual and asexual
Heterotrophic
Timeline of Important Milestones in Microbiology
1875
Ferdinand J. Cohn contributes to the founding of the science of bacteriology. He
publishes an early classification of bacteria using the genus name Bacillus for the
first time.
1876
Robert Koch publishes a paper on his work with anthrax, pointing explicitly to a bacterium as
the cause of this disease. This validates the germ theory of disease. His work on anthrax was
presented and his papers on the subject were published under the auspices of Ferdinand Cohn.
1884
tubercle
proved by
cultivation
tuberculosis
Medicine or
Robert Koch puts forth a set of postulates, or standards of proof, involving the
bacillus. Koch's postulates are published in The Etiology of Tuberculosis, in which he
demonstrated three major facts: 1) the presence of the tubercule bacillus (as
staining) in tubercular lesions of various organs of humans and animals, 2) the
of the organisms in pure culture on blood serum, and 3) the production of
at will by its inoculation into guinea pigs. Koch was awarded the Nobel Prize in
Physiology in
1905.
1890
Sergei Winogradsky succeeds in isolating
1890-1891, Winogradsky performs the
the process of nitrification in nature.
nitrifying bacteria from soil. During the period
definitive work on the organisms responsible for
1891
Paul Ehrlich proposes that antibodies are responsible for immunity. He shows that
antibodies form against the plant toxins ricin and abrin. With Metchnikoff, Ehrlich
awarded the Nobel Prize in Medicine or Physiology in 1908.
is jointly
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1892
Dmitri Ivanowski publishes the first evidence of the filterability of a pathogenic agent, the virus of
tobacco mosaic disease, launching the field of virology. He passes the agent through candle filters
that retain bacteria, but he isn't sure that the agent is a unique organism.
1912
Paul Ehrlich announces the
first specific chemotherapeutic
derivative and finally the 606th
London, where Alexander
discovery of an effective cure (Salvarsan) for syphilis, the
agent for a bacterial disease. Ehrlich was seeking an arsenic
compound worked. He brought news of the treatment to
Fleming became one of the few physicians to administer it.
1915
Frederick Twort announces the first discovery of bacteriophages, or bacteria-infecting viruses.
Twort’s discovery was something of an accident. He had spent several years growing viruses and
noticed that the bacteria infecting his plates became transparent, indicating that they had been
lysed or broken open and destroyed. Felix d’Herrelle independently describes bacterial
viruses and coins the term “bacteriophage.”
1928
Frederick Griffith discovers transformation in bacteria and establishes the
foundation of molecular genetics. He shows that injecting mice with a mixture of
live,
avirulent, rough Streptococcus pneumoniae Type I and heat-killed, virulent
smooth
S. pneumoniae Type II, leads to the death of the mice. Live, virulent, smooth S. pneumoniae Type II are isolated
from the dead mice.
1929
Alexander Fleming publishes the first paper describing penicillin and its effect on grampositive microorganisms. This finding is unique since it is a rare example of bacterial lysis and
not just microbial antagonism brought on by the mold Penicillium. Fleming kept his cultures 23 weeks before discarding them. When he looked at one set he noticed that the bacteria seemed
to be dissolving and the mold was contaminating the culture. When penicillin is finally
produced in major quantities in the 1940s, its power and availability effectively launch the “Antibiotics Era,” a
major revolution in public health and medicine. With Florey and Chain, Fleming is awarded the Nobel Prize in
Medicine or Physiology in 1945.
1935
Gerhard J. Domagk uses a chemically
synthesized anti-metabolite, Prontosil, to
kill Streptococcus in mice. One of the first
patients to be treated with Protonsil is
Domagk’s daughter who has a streptococcal infection that is unresponsive to other treatments. Near death, she
is injected with large quantities of Protonsil and makes a dramatic recovery. Domagk is awarded the Nobel
Prize in Medicine or Physiology in 1939.
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1944
Oswald Avery, Colin MacLeod, and Maclyn McCarty show that DNA is the transforming
material in cells. They demonstrate that the transformation of Streptococcus pneumoniae from
an avirulent type to a virulent type is the result of the transfer of DNA from dead smooth
organisms to live rough ones. They also show that the transforming principle is destroyed by
pancreatic deoxyribonuclease —an enzyme that hydrolyzes DNA —but is not affected by
pancreatic ribonuclease or enzymes that destroy proteins.
1944
Albert Schatz, E. Bugie and Selman Waksman
used against tuberculosis. Streptomycin has the same
negative microorganisms as penicillin does on gramthe Nobel Prize in Medicine or Physiology in 1952.
discover streptomycin, soon to be
specific antibiotic effect against grampositive ones. Waksman is awarded
1946
Joshua Lederberg and Edward L. Tatum publish the first paper on a type of bacterial mating called
conjugation. The proof is based on the
generation of daughter cells able to grow in
media that cannot support growth of
either of the parent cells. Their experiments
showed that this type of gene exchange
requires direct contact between bacteria. At
the time Lederberg began studying with Tatum, scientists believed that bacteria reproduced asexually, but from
the work of Beadle and Tatum, Lederberg knew that fungi reproduced sexually and he
suspected that bacteria did as well.
1949
Microbiologist John Franklin Enders, virologist Thomas H. Weller and physician
Frederick Chapman Robbins together develop a technique to grow poliovirus in test
cultures of human tissues. This approach gave virologists a practical tool for the
isolation and study of viruses. Enders, Weller and Robbins were awarded the Nobel
Prize in Medicine or Physiology in 1954.
tube
1952
Joshua Lederberg and Norton Zinder report on transduction, or transfer of genetic
information to cells by viruses. They show that a phage of Salmonella typhimurium can carry
DNA from one bacterium to another.
1952
Alfred Hershey and Martha
Chase suggest that only DNA is
needed for viral replication.
Using radioactive isotopes 35S to
track protein and 32P to track DNA, they show that progeny T2 bacteriophage isolated from lysed bacterial
cells have the labeled nucleic acid. Further, most of the labeled protein doesn’t enter the cells but remains
attached to the bacterial cell membrane.
1960
Francois Jacob, David Perrin, Carmen Sanchez and Jacques Monod propose the operon
concept for control of bacteria gene action. Jacob and Monod later propose that a protein
repressor blocks RNA synthesis of a specific set of genes, the lac operon, unless an inducer,
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lactose, binds to the repressor. With Lwoff, Jacob and Monod are awarded the Nobel Prize in Medicine or
Physiology in 1965.
1973
Stanley Cohen, Annie Chang, Robert Helling and Herbert Boyer
show that
extrachromosomal bits of DNA called plasmids act as vectors for
maintaining cloned
genes in bacteria. They show that if DNA is broken into fragments
and combined with
plasmid DNA, such recombinant DNA molecules will reproduce if inserted into bacterial cells. The discovery is
a major breakthrough for genetic engineering, allowing for such advances as gene cloning and the modification
of genes.
1977
Carl Woese uses ribosomal RNA analysis to recognize a third form of life, the Archaea,
whose genetic makeup is totally different from the regular bacteria. He is the creator of the
three branch evolutionary tree.
1979
Smallpox (variola) is declared officially eliminated, the last naturally occurring case having been
seen in 1977 in Somalia. Small quantities remain held under tightly controlled conditions in the U.S. and former
U.S.S.R. Smallpox is the only microbial disease to ever have been deliberately eradicated.
1982
Stanley Prusiner finds evidence that disease can be caused by a class of infectious proteins
he call prions. These abnormal proteins cause scrapie, a fatal neurodegenerative disease of
sheep. Prusiner is awarded the Nobel Prize in Medicine or Physiology in 1997.
1983
Luc Montagnier and Robert Gallo announce their discovery of the immunodeficiency
virus (HIV) believed to cause AIDS.
1986
Kary Mullis uses a heat stable enzyme from Thermus aquaticus to establish polymerase chain
reaction technology. PCR is used to amplify target DNA many-fold. Mullis is awarded the
Nobel Prize in Chemistry in 1993.
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1995
Craig Venter, Hamilton Smith, Claire Fraser and colleagues at TIGR elucidate the
first complete genome sequence of a microorganism: Haemophilus influenza.
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