Prescott’s Microbiology, 9th Edition
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The Evolution of Microorganisms and Microbiology
CHAPTER OVERVIEW
This chapter introduces the field of microbiology and discusses the importance of microorganisms not only as
causative agents of disease, but also as important contributors to food production, antibiotic manufacture,
vaccine development, and environmental management. It presents a brief history of the science of
microbiology and an overview of the microbial world. The origin of life and microbial evolution is put in the
context of microbial phylogenies.
LEARNING OUTCOMES
After reading this chapter you should be able to:
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differentiate the biological entities studied by microbiologists from those studied by other biologists.
explain Carl Woese’s contributions in establishing the three domain system for classifying cellular life
provide an example of the importance to humans of each of the major types of microbes.
determine the type of microbe (e.g. bacterium, fungus, etc) when given a description of a newly
discovered microbe
propose a time line of the origin and history of microbial life and integrate supporting evidence into it
design a set of experiments that could be used to place a newly discovered cellular microbe on a
phylogenetic tree based on small subunit (SSU) rRNA sequences
compare and contrast the definitions of plant and animal species, microbial species and microbial strains
evaluate the importance of the contributions to microbiology made by Hooke, Leewenhoek, Pasteur,
Koch, Cohn, Beijerinck, von Behring, Kitasato, Metchnikoff and Winogradsky
outline a set of experiments that might be used to decide if a particular microbe is the causative agent of a
disease
predict the difficulties that might arise when using Koch’s postulates to determine if a microbe causes a
disease unique to humans
construct a concept map, table or drawing that illustrates the diverse nature of microbiology and how it
has improved human conditions
support the belief held by many microbiologists that microbiology is experiencing its second golden age
CHAPTER OUTLINE
I.
II.
Members of the Microbial World
A. Microbiology is the study of organisms too small to be clearly seen by the unaided eye (i.e.,
microorganisms); these include viruses, bacteria, archaea, protozoa, algae, and fungi
B. Some microbes (e.g., algae and fungi) are large enough to be visible, but are still included in the
field of microbiology; while these may be multicellular organisms, differentiated tissues are absent
C. Prokaryotes have a relatively simple morphology and lack a true membrane-delimited nucleus
D. Eukaryotes are morphologically complex and have a true, membrane-enclosed nucleus
E. The work of Carl Woese and his collaborators suggests that organisms fall into one of three domains
based on nucleotide sequence similarities among small subunit ribosomal RNAs (SSU rRNAs)
1. Eukarya—contains all eukaryotic organisms; have a complex membranedelimited organelle structure
2. Bacteria—diverse and widespread prokaryotes; cell walls contain peptidoglycan
3. Archaea—prokaryotes with cell walls that lack peptidoglycan; have unique membrane lipids
F. Viruses, viroids, virusoids, and prions are not composed of cells and not part of the domain
classification scheme
Microbial Evolution
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Prescott’s Microbiology, 9th Edition
A.
Evidence for the origin of life
1. Earth is about 4.6 billion years old; what appear to be the fossilized remains of 3.5-billionyear-old prokaryotic cells have been found in stromatolites and sedimentary rocks
2. Extant organisms have been suggested to contain structures and molecules that are relics of
ancient life forms
B. RNA world
1. It is speculated in the RNA world theory that the first self-replicating molecules were RNAs
that stored information and had catalytic activity (ribozymes); eventually DNA became the
molecule for information storage and proteins became the molecules with catalytic activity
2. The earliest prokaryotes were probably anaerobic and lithotrophs
3. Cyanobacteria probably developed oxygenic photosynthesis 2.5 billion years ago forming
layered rocks called stromatolites (stratified rocks that are formed by incorporation of mineral
sediments into microbial mats)
C. Evolution of the three domains of life
1. The universal phylogenetic tree is based on comparisons of small subunit rRNA molecules
such that evolutionary distances are shown
2. The last universal common ancestor (LUCA) sits at the root of the tree on the bacterial branch;
the nature of this organism is unclear
3. The endosymbiotic origin of mitochondria, chloroplasts, and hydrogenosomes
a. Endosymbiotic theory states that these organelles arose from prokaryotes that lived
within eukaryotic cells, eventually losing parts of their genome to the host cell and
thereby losing the ability to survive independently; organelles have both circular
chromosomes related to bacterial genomes and independent transcription and translation
systems
b. The hydrogen hypothesis states that the progenitor of mitochondria was a bacterium that
produced hydrogen through fermentation that was required by the host; the
hydrogenosome may be another relic of this early symbiont
4. Cellular life forms developed through the same evolutionary processes seen today including
mutation and horizontal gene transfer
5. Since prokaryotic organisms generally do not reproduce sexually, species are defined as
groups of strains (pure cultures) sharing stable distinguishing properties; microbiologists use
the binomial system for naming species
III. Microbiology and Its Origins
A. Microscopy and the discovery of microorganisms
1. Invisible living creatures were thought to exist and were thought to be responsible for disease
long before they were observed; the field of microbiology developed as the tools used to study
microbes developed
2. Antony van Leeuwenhoek (1632–1723) constructed microscopes and is credited as the first
person to observe and describe microorganisms accurately; Robert Hooke published the first
drawings of microorganisms
B. Culture-based methods for studying microorganisms
1. Spontaneous generation
a. The proponents of the concept of spontaneous generation claimed that living organisms
could develop from nonliving or decomposing matter
b. Francesco Redi (1626–1697) challenged this concept by showing that maggots on
decaying meat came from fly eggs deposited on the meat, and not from the meat itself
c. John Needham (1713–1781) showed that mutton broth boiled in flasks and then sealed
could still develop microorganisms, which supported the theory of spontaneous
generation
d. Lazzaro Spallanzani (1729–1799) showed that flasks sealed and then boiled had no
growth of microorganisms, and he proposed that air carried germs to the culture medium;
he also commented that external air might be needed to support the growth of animals
already in the medium; the latter concept was appealing to supporters of spontaneous
generation
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Prescott’s Microbiology, 9th Edition
e.
C.
D.
E.
F.
G.
Theodore Schwann (1810–1882) and others carried out experiments testing the need for
air if growth was to occur
f.
Louis Pasteur (1822–1895) heated the necks of flasks, drawing them out into long curves,
sterilized the media, and left the flasks open to the air; no growth was observed because
particles carrying organisms did not reach the medium, instead they were trapped in the
neck of the flask; if the necks were broken, particles would enter the flasks and the
organisms would grow; in this way Pasteur disproved the theory of spontaneous
generation
g. John Tyndall (1820–1893) demonstrated that dust carried microbes and that if dust was
absent, the broth remained sterile—even if it was directly exposed to air; Tyndall also
provided evidence for the existence of heat-resistant forms of bacteria
Microorganisms and disease
1. Agostino Bassi (1773–1856) showed that a silkworm disease was caused by a fungus, the first
demonstration of microbes causing disease
2. Louis Pasteur showed that the pébrine disease of silkworms was caused by a protozoan parasite;
he demonstrated that alcoholic fermentations were performed by yeasts under anaerobic
conditions and that different fermentation products were produced by different
microorganisms; he developed the process of pasteurization used to preserve wine and milk
during storage
3. Joseph Lister (1872–1912) developed a system of surgery designed to prevent microorganisms
from entering wounds; his patients had fewer postoperative infections, thereby providing
indirect evidence that microorganisms were the causal agents of human disease; his published
findings transformed the practice of surgery
Koch's postulates
1. Robert Koch (1843–1910), using criteria developed by his teacher, Jacob Henle (1809–1895),
established the relationship between Bacillus anthracis and anthrax; his criteria became known
as Koch’s postulates and are still used to establish the link between a particular microorganism
and a particular disease:
a. The microorganism must be present in every case of the disease, but absent from healthy
individuals
b. The suspected microorganism must be isolated and grown in pure culture
c. The same disease must result when the isolated microorganism is inoculated into a
healthy host
d. The same microorganism must be isolated again from the diseased host
2. Koch’s work with anthrax was independently confirmed by Pasteur
Pure culture methods
1. Koch and his associates developed techniques, reagents, and other materials for culturing
bacterial pathogens on solid growth media; agar plates enable microbiologists to isolate
microbes in pure culture
2. Charles Chamberland (1851–1908) constructed a bacterial filter that removed bacteria and
larger microbes from specimens; this led to the discovery of viruses as disease-causing agents
Immunology
1. Edward Jenner used a vaccination procedure to protect individuals from smallpox
2. Louis Pasteur developed other vaccines including those for chicken cholera, anthrax, and
rabies
3. Emil von Behring (1854–1917) and Shibasaburo Kitasato (1852–1931) induced the formation
of diphtheria-toxin antitoxins in rabbits; the antitoxins (actually antibodies) were effectively
used to treat humans and provided evidence for humoral (antibody) immunity
4. Elie Metchnikoff (1845–1916) described phagocytic cells in the blood, thus demonstrating
cell-mediated immunity
Microbial ecology
1. Sergei Winogradsky (1856–1953) worked with soil bacteria and discovered that they could
oxidize iron, sulfur, and ammonia to obtain energy; he also studied anaerobic nitrogen fixation
and cellulose decomposition
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in any manner. This document may not be copied, scanned, duplicated, forwarded, distributed, or posted on a website, in whole or part.
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Prescott’s Microbiology, 9th Edition
2.
Martinus Beijerinck (1851–1931) isolated aerobic nitrogen-fixing bacteria, a root-nodule
bacterium capable of fixing nitrogen, and sulfate-reducing bacteria
3. Beijerinck and Winogradsky pioneered the use of enrichment cultures and selective media to
isolate microorganisms that can eat and/or breathe inorganic minerals
IV. Microbiology Today
A. Research in both basic and applied microbiology has an impact on many fields including medicine,
agriculture, food science, ecology, genetics, biochemistry, and molecular biology
B. Molecular and genomic methods of studying microbes
1. Manipulating DNA in microorganisms is central to studying their
relationships and nature
2. The genome (all the genetic information) of an organism can be analyzed
using methods leading to determination of the base sequence of genes
3. Genomic analysis defines functions of genes, their regulation, and how
they form biological systems
C. Major fields in microbiology
1. Medical microbiology - the study of infectious disease in humans and
animals, identifying the causative agents and planning measures for their
control
2. Public health microbiology and epidemiology - the study of the
mechanisms by which diseases spread and the monitoring of the amount
of disease in populations
3. Immunology - study of how the body's immune system protects against
infectious disease; includes the study of allergies and autoimmune
diseases
4. Microbial ecology - study of the ecological role of microbes in
biogeochemical cycles and the interaction of microbes with each other
and their habitat
5. Agricultural microbiology - study of the impact of microbes on
agriculture, including aspects of nutrient cycles, animal husbandry, and
plant pathogens
6. Food and dairy microbiology - study of the use of microbes in food
production, food spoilage, and food-borne diseases
7. Industrial microbiology - study of the use of microorganisms in the
manufacture of antibiotics, vaccines, chemicals, enzymes, vitamins, and
other products
D. More basic research fields of microbiology include microbial physiology,
microbial genetics, molecular biology, and bioinformatics
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in any manner. This document may not be copied, scanned, duplicated, forwarded, distributed, or posted on a website, in whole or part.
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Prescott’s Microbiology, 9th Edition
CRITICAL THINKING
1.
Discuss the spontaneous generation theory. Present the evidence that was used to support it and present
the evidence that was used to discredit it. How was this theory finally discredited?
2.
Describe in detail at least two ways in which microorganisms have a direct and substantial impact on your
life (other than as causative agents of disease). Include a discussion of the role(s) of the microorganisms
in these processes.
3.
In the 1980s when AIDS was first recognized, scientists were faced with the task of identifying the
causative agent. Suppose you were one of those scientists and that you observed a virus in the tissues of
AIDS patients. Which steps of Koch’s postulate could you use to support your belief that the virus was
responsible for the disease? Which steps couldn’t you use? Explain your answers.
4. Comment on why the science of immunology is often discussed and grouped with studies of
microbiology.
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© 2014 by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution
in any manner. This document may not be copied, scanned, duplicated, forwarded, distributed, or posted on a website, in whole or part.
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