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CHAPTER
The Microbial World
1
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PRINTED PDF | ORIGINAL DIRECTLY FROM THE PUBLISHER | 100% Summary
VERIFIED ANSWERS | DOWNLOAD IMMEDIATELY AFTER THE ORDER Chapter 1 introduces the study of microbiology for students, most of whom will
have had little or no exposure to the subject. Consequently, you have a good
opportunity to provide an overview of microbiology that demonstrates the
A+
important roles microorganisms (or microbes) play in human activities and in the
ecology of the entire biosphere. The ability of microorganisms to exist
independently in nature as free-living cells within larger microbial communities
(Figure 1.1) confers enormous adaptive advantages over cells of macroorganisms,
which are incapable of an independent existence.
BROCK BIOLOGY ОР
MICROORGANISMS 1.1 | Microorganisms, Tiny Titans of the Earth
Describe to students ways in which microbiology serves as both a basic and an applied
biological science. From a basic perspective, the study of microorganisms in laboratory
culture has been the primary means by which the fundamental genetic and biochemical
MADIGAN BENDER BUCKLEY SATTLEY STAHL properties of living cells have been revealed. From an applied perspective, microorganisms
directly affect the quality of human life in both detrimental and beneficial ways. Although
microorganisms are the causative agents of some of the most important human, animal, and
plant diseases, they are also used for the industrial production of antibiotics,
SOLUTIONS
pharmaceuticals, and foods. Microbes are also increasingly being used for beneficial
purposes as diverse as bioremediation of polluted sites, gene therapies for genetic diseases,
and the production of biofuels. Microbiology is therefore a science of far-reaching scope,
with applications that affect the quality of human life in a variety of ways (Figure 1.2).
MYNURSYTEST.STORE You should also emphasize to students the importance of microorganisms in the
emergence and maintenance of higher forms of life. From the production of molecular
oxygen (by cyanobacteria) to the biogeochemical cycling of key elements, such as carbon,
nitrogen, and sulfur, microorganisms play a major role in sustaining all life on the planet.
Point out in your course introduction that for all the reasons summarized in this section,
microbiology is the foundation of all biological sciences.
1.2 | Structure and Activities of Microbial Cells
Because microorganisms generally exist as free-living cells, it is important to discuss the
characteristics of cells in general. Emphasize that all cells exhibit a nonrandom organization with a
?
semipermeable membrane boundary that encompasses an internal system that is not in equilibrium
with its environment. Point out that prokaryotic cells (i.e., all Bacteria and Archaea) do not contain
membrane-bound, internal organelles as traditionally described for eukaryotic cells (the Eukarya;
Figure 1.4). In particular, the organization of prokaryotic DNA as a single chromosome in an
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arrangement called a nucleoid, an aggregated mass of genetic material within the cytoplasm, is in slower growing diploid cells. This allows for greater adaptive potential through rapid selection
stark contrast to the compartmentalized, multichromosomal configuration typically found in for advantageous mutations and counterselection against deleterious mutations.
eukaryotes. However, despite the structural and morphological similarities of Bacteria and Archaea, The theoretical lower limit of size for a living cell is likely near 0.2 μm in diameter. This limit
make sure your students are aware early on that these groups of microorganisms have quite distinct
is dictated by the amount of volume required to contain cellular components that are crucial
evolutionary lineages and are, therefore, not closely related on a genetic level. This concept is
for maintaining life, such as (1) the presence of essential genes on the chromosome; (2)
discussed in more detail in Section 1.5.
having a sufficient number of ribosomes; and (3) containing a minimal number of metabolic,
The ability of cells to maintain a thermodynamic energy flow far from equilibrium
structural, and transport proteins within the cell. Challenge students to list these and other
defines what we refer to as a living system. All living systems display some form of
molecular components that a cell would have to contain to maintain life. Remind students
enzyme-driven metabolism in which both energy-yielding (catabolic) and energy-
consuming (anabolic) biochemical reactions are catalyzed concurrently. These chemical that some cells are parasitic in nature. Inform them that, much like viruses, such
transformations allow for biosynthesis of new cell structures and, ultimately, cell division microorganisms often have streamlined genomes that lack important genes and may make
(microbial growth). Figure 1.5 shows the characteristics that define cellular life, some of them dependent upon their hosts for growth. Can such organisms truly be considered living?
which are universal (e.g., metabolism and evolution) and some of which occur only in This might make a good outside project for group debate, requiring students to view the cell
some cells (e.g., differentiation and motility). as a three-dimensional physical structure constrained in space and to research a problem
that is currently being debated.
1.3 | Cell Size and Morphology Using Figure 1.8, point out the three major morphologies of prokaryotic cells (coccus, rod, and
spirillum). Inform your students that, in some species, the cells remain attached following cell
The presentation in the text of the significance of being small is an important concept for students division, giving rise to different arrangements that are often genus-specific. For example, coccus
to internalize as they begin their study of microbiology. Table 1.1 shows the wide size range cells may exist as long chains (Streptococcus) or grapelike clusters (Staphylococcus). Less
variability of bacterial cells, which range from a diameter of about 0.2 µm to over 700 µm. Use the common cell morphologies also exist, such as spirochetes, appendaged (budding) bacteria, and
two examples of unusually large bacteria discussed in this section to illustrate the current upper filamentous bacteria (Figure 1.8). Stress to students that these morphologies are only representative
limit of bacterial cell size: (1) the surgeonfish gut symbiont Epulopiscium fishelsoni (>600 µm in of those found in nature. Other unusual shapes have also been described in rare cases (e.g., square-
length; Figure 1.6a), and (2) the sulfur chemolithotroph Thiomargarita namibiensis (750 µm; and star-shaped cells!).
Figure 1.6b). The evolutionary “rationale” for the existence of unusually large-celled bacteria is a Before the molecular era, morphological and physiological properties were used to classify
mystery when one considers that the metabolic rate of a cell varies inversely with the square of its bacterial species. However, we now know that these criteria are poor predictors of evolutionary
size. Ask your students for ideas and/or hypotheses that might explain the selective advantage of relationships. For example, certain species of Archaea may appear identical in size and shape to
large cell size in these two prokaryotes. species of Bacteria under the microscope, but these organisms are of different phylogenetic
The fact that bacteria can live independently as single cells (unlike an individual cell of a domains and thus are not closely related to one another on an evolutionary basis. The cell
multicellular organism) suggests that they must possess some capabilities that provide a selective morphology of a particular species is primarily a result of selective pressures in a given habitat that
advantage over their multicellular counterparts that ensure their survival on the planet. Small cells favored a particular cell shape for enhanced reproductive success.
have more surface area to volume (i.e., a higher surface-to-volume ratio), and this alone confers
many of the evolutionary advantages of being small, including the following: 1.4 | An Introduction to Microbial Life
● Rapid nutrient and waste transport into and out of the cell allows for faster metabolic rates and
growth rates. This section of the chapter provides an overview of the key factors that distinguish cells of the
● Rapid growth rates result in the rapid production of large populations of cells. These different domains of life, and how these are further distinguished from acellular microbes—the
populations, in turn, can greatly affect the physiochemical conditions of an ecosystem within a viruses. Figure 1.9 beautifully compares the size relationships of a variety of microbial forms and
short time period. components, from the uncommonly large bacterium Epulopiscium fishelsoni at a length of 600 μm
● Transport rates are a function of the surface area of the cytoplasmic membrane relative to cell (see also Figure 1.6) to individual proteins at the limit of resolution of an electron microscope
volume. Use Figure 1.7 to mathematically demonstrate to students that the surface area of a (0.2 nm). Mention the following key points:
sphere is a function of the square of the radius, whereas the volume of a sphere is a function of the ● The greatest diversity of Bacteria and Archaea has never been cultured in the laboratory, and
cube of the radius. This means that the surface-to-volume ratio of a spherical cell can be such species are known only by their DNA sequences found in environmental samples.
expressed as 3/r, where r equals the radius of the cell. Therefore, a coccus cell having a smaller ● Although they both have a prokaryotic cell structure, Bacteria and Archaea are not closely
radius has more surface area per volume and, thus, more efficient transport capabilities, than a related. On a molecular level, Archaea have much in common with the eukaryotes.
coccus cell having a larger radius. ● The metabolic and physiological diversity of microorganisms, especially the Bacteria and
● Rates of evolutionary change are higher in smaller, faster growing haploid cells than in larger, Archaea, is astonishing, with species capable of aerobic respiration, anaerobic respiration,
2 INSTRUCTOR'S MANUAL FOR BROCK BIOLOGY OF MICROORGANISMS, 16e Copyright © 2021 Pearson Education, Inc. Copyright © 2021 Pearson Education, Inc. CHAPTER 1 The Microbial World 3
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fermentation, and/or phototrophy inhabiting nearly every imaginable habitat on Earth. microorganisms “simple,” insignificant creatures that only cause disease—and will set the
● Microorganisms of the domain Eukarya include the fungi, protists (including the protozoa and stage for more detailed study in future chapters.
algae), and helminths (roundworms and flatworms). Finally, point out that microorganisms can be found in even the most inhospitable
environments by human standards. Students are often amazed at the extreme conditions in
● The Eukarya lineage is evolutionarily younger than either the Bacteria or the Archaea.
which microorganisms can thrive (Table 1.2). Point out that even in punishingly harsh
● Because viruses are acellular and incapable of autonomous reproduction, most microbiologists ecosystems, such as in volcanic hot springs or freezing Antarctic lakes, microbes called
consider them to be nonliving biological entities. extremophiles are able to exist or even thrive in conditions that define the physiochemical
● Viral genomes may be either DNA or RNA, but not both. Whether DNA or RNA, their limits to life on Earth. These communities contain a reservoir of genetic diversity that is
genomes may be single- or double-stranded. All cells have double-stranded DNA genomes. largely unexplored and that could benefit humankind in as yet unknown ways.
● Viruses also display incredible diversity, despite the fact that they are nonliving, with broad
host ranges. Viruses are known to infect cells from all three domains of life. 1.6 | The Impact of Microorganisms on Human Society
Students probably understand the importance of microorganisms as agents of infectious disease,
1.5 | Microorganisms and the Biosphere and indeed, this has been a driving force in the development of microbiology as a distinct
scientific discipline. The effects of microorganisms upon human affairs have been remarkable,
Although Earth is believed to be about 4.6 billion years old, several lines of evidence particularly when one compares the foremost causes of death in the United States at the
indicate that the appearance of multicellular life did not occur until about 600 million years beginning of the twentieth century (before the widespread use of antibiotics and vaccines) with
ago (Figure 1.10). By contrast, microbial cells (single-celled prokaryotes) likely appeared the major causes of death in this century (Figure 1.13). While the deleterious effects of
between 3.8 and 3.9 billion years ago and therefore were the only inhabitants of the planet pathogenic bacteria to human wellness should be discussed here, it is important to also stress the
for about 80% of its history! The appearance of multicellular life was necessarily preceded key beneficial roles microorganisms play in agriculture (Figure 1.14), in human digestive health
by the accumulation of significant amounts of molecular oxygen (O2) in the atmosphere, a (Figure 1.15), in the food and beverage industries (Figure 1.16), and in the growing fields of
phenomenon that resulted from the activity of cyanobacteria and the evolution of a biotechnology and alternative and renewable energy (Figure 1.17). With this discussion, students
chlorophyll molecule that could use water (H2O) as electron donor (see Chapter 13). should become aware of the tremendous influence of microorganisms in human society.
Develop this concept for students in some detail at an early stage in the course to provide The genomes of microorganisms hold incredible potential for the production of useful and
proper historical perspective of important events in cellular evolution. You may wish to valuable products. The traditional methods of employing microorganisms for human use (e.g.,
start with the evidence supporting the hypothesis that the first self-replicating “entities” fermentation) have evolved into the large-scale, commercial ventures of industrial microbiology
may have been RNA molecules, and the incorporation of these entities within lipid and biotechnology. Whereas industrial microbiology exploits microbial activities in the
membranes may have represented the first cell type(s). This topic will be more thoroughly production of large quantities of lower cost commodities, such as solvents and enzymes, the
discussed in Chapter 13. “biotech” industry uses genetically engineered microorganisms to produce smaller quantities of
Discuss with your students some of the events that led to multicellular forms of life. The specialized products of high value, such as certain pharmaceuticals. An excellent example is the
evolution of anaerobic phototrophic metabolisms likely began within 500 million years production of human insulin by Escherichia coli, an innovation that made the treatment of
after the appearance of the first cells, followed nearly a billion years later by the evolution
diabetes affordable for people from all economic backgrounds. In addition to producing a product
of cyanobacteria from these early phototrophs (Figure 1.11), thus starting the slow process
directly, bacterial cells can be used as a vehicle to introduce specific genes into the genomes of
of oxygenating the atmosphere and the evolutionary path to multicellularity.
other organisms for commercial production of a desired product. For example, genetic
Impress upon your students the enormous abundance of microorganisms in the
engineering of Agrobacterium tumefaciens, a plant pathogen that naturally transfers DNA
biosphere; the total number of microbial cells on Earth is estimated to be about eight orders
directly into plant cells upon infection, has led to the use of plants for the production of human
of magnitude greater than the number of stars in the universe! Emphasize that this vast
antibodies that have potential anticancer or antiviral properties.
quantity of microbial biomass sequesters more life-sustaining nutrients (e.g., carbon,
One area of extensive research in industrial microbiology is the production of biofuels. These
nitrogen, and phosphorus) than all plants and animals combined (Figure 1.12).
products are often used to supplement petroleum-based fuels and may include methane, ethanol,
Introduce the students to microbial ecology, the exciting subdiscipline of microbiology
biodiesel, hydrogen (H2), and other fuels derived from microbial metabolisms. Microorganisms
that focuses on the interactions and influence of microbial communities on the macroscopic
are also being used extensively to restore polluted natural areas in a process called
world around them. The biochemical conversions and molecular interactions of
bioremediation. By applying specific microorganisms (or nutrients to stimulate their growth) to
microorganisms significantly control the balance and community structure of all living
polluted sites, contaminants such as pesticides, heavy metals, and crude oil and other
organisms in an ecosystem. In fact, the very existence of multicellular life depends upon
hydrocarbons can all be cleaned successfully and thoroughly.
the nutrient cycling activities of microorganisms. The effect of microbes on animals,
plants, and global ecosystems is a topic interwoven throughout a number of chapters in the
text. These concepts will come as a surprise for most students—who generally consider
4 INSTRUCTOR'S MANUAL FOR BROCK BIOLOGY OF MICROORGANISMS, 16e Copyright © 2021 Pearson Education, Inc. Copyright © 2021 Pearson Education, Inc. CHAPTER 1 The Microbial World 5
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1.7–1.10 | Microscopy and the Origins of Microbiology 1.11 | Pasteur and Spontaneous Generation
It is important to emphasize the historical roots of microbiology, particularly considering its As a young researcher, Louis Pasteur was formally trained as a chemist with expertise in the
rather recent beginnings as a systematic field of science in the nineteenth century and the fact field of crystallography. His knowledge of the optical properties of crystals provided the
that several new fields have arisen from this discipline (e.g., molecular biology and basis for his early investigations into the biological sciences. Begin the discussion of his
biotechnology). Lead the students on a chronological journey, beginning with Robert celebrated scientific achievements by pointing out that it was his observation that living
Hooke’s first description of a microorganism (a fungal mold) in 1665 (Figure 1.18) and organisms discriminate between optical isomers of metabolites during growth (Figure 1.30)
Antoni van Leeuwenhoek’s microscope and publication of the first observation of bacteria in that led him to begin a series of experiments that would result in the defeat of the centuries-
1684 (Figure 1.19). old theory of spontaneous generation. Pasteur’s experimental design that finally disproved
Following your introduction of the pioneers of microscopy, provide the students with an this theory introduced the now famous swan-necked flask (Figure 1.31). His work is a
overview of microscopic methods in common usage today. The variety of methods available classic example of the effectiveness of using the scientific method and controlled
for observing microorganisms must be introduced early, as much of the presentation of experimentation to resolve questions rather than personal observation and interpretation,
structure–function relationships depends upon the excellent micrographs that appear throughout which often lead to unsubstantiated (and often erroneous) conclusions. Point out to students
the book. Although details of microscopy are more easily introduced in the laboratory portion that disproving spontaneous generation resulted in the development of effective procedures
of the course, the material included here is pertinent to effective lecture presentation. for controlling microbial growth, including the familiar process of pasteurization. Outline
● Discuss the basic principles and components of the compound light microscope, the major career accomplishments of Pasteur, pointing out the fact that although his
including the relationships between resolution and magnification, and numerical professional training pertained to chemistry rather than biology, his laboratory
aperture (Figure 1.20). Note that although bright-field microscopy is fine for visualizing experimentation led him to the study of microorganisms.
pigmented cells (Figure 1.21), it is not an efficient tool for viewing unstained cells with ● As a chemist, Pasteur’s work with optical isomers of amyl alcohol, a byproduct of
no natural pigmentation, such as nonphototrophic bacteria. alcohol fermentation by beets, led him to confirm that fermentation was not a strictly
● This deficiency will lead to a discussion of various methods employed to increase chemical phenomenon but that living yeast cells were required for the process. The
contrast. Discuss the various simple dyes used to stain cells, most of which are outcome of his fermentation studies led him to the classic experiments that defeated
positively charged, basic dyes capable of binding to negatively charged cell surfaces spontaneous generation (Figure 1.31).
(e.g., methylene blue and crystal violet; Figure 1.22). Continue the discussion of ● Discuss the many other accomplishments of Pasteur, including the development of
differential stains, the most widely used of which is the Gram stain (Figure 1.23). vaccines for anthrax, fowl cholera, and rabies. The dramatic results of his rabies
● Students should understand that while staining procedures increase the contrast of cells vaccine, which saved a young boy, startled the scientific world and led the French
against the background to make them more visible, they also kill cells and may distort government to build the Pasteur Institute in Paris in 1888 (Figure 1.32). Together with
their appearance. Discuss phase-contrast microscopy and dark-field microscopy (Figure Robert Koch, whose scientific achievements are discussed next, Pasteur played a major
1.24), two tools that allow one to look at living cells without the need for staining. role in establishing the field of medical microbiology.
● Fluorescence microscopy is widely used in clinical diagnostic microbiology and
environmental microbiology (Figure 1.25). Most students who enter the biotechnology 1.12 | Koch, Infectious Diseases, and Pure Cultures
industry or medical profession will work with fluorescent molecules (such as those used
for fluorescence antibody staining methods). The variety and sensitivity of these Explain to your students that for centuries many thought that some unknown agent from a diseased
molecules have increased dramatically over the past decade. This has allowed the person could be transmitted to healthy people, but no real proof of this existed until the work of
development of a wide variety of nonradioactive alternatives to biological assays that Robert Koch (Figure 1.33). Although Koch was 21 years younger than Pasteur, several of their
are now routinely used in research. greatest achievements were carried out around the same time during the late 1800s. The following
● Students should be interested in the micrographs from three-dimensional imaging of list serves as an introduction to the works of Koch for your students.
cells. Depending upon the level of the course, you may choose to discuss the principles ● Koch’s work on the germ theory of disease (1876) was perhaps the most important stimulus
of differential interference contrast microscopy (Figure 1.26) and confocal scanning for the development of medical microbiology. Given the focus on bioterrorism in recent
laser microscopy (Figure 1.27). Lastly, show and discuss the micrographs obtained from years, students may find it interesting that Koch’s work leading to this important theory
electron microscopy (Figures 1.28 and 1.29). Note the differences between scanning involved the study of the endospore-forming bacterium Bacillus anthracis, the causative
electron microscopy (SEM), which provides an image of the external features of a agent of anthrax. Carefully discuss Koch’s postulates, the use of which has since led to
specimen, and transmission electron microscopy (TEM), in which thin sections of the discoveries for the prevention and cure of many infectious diseases (Figure 1.33). However,
specimen show its detailed internal structure. be sure to note that while Koch’s postulates are the “gold standard” for determining the
causative agent of a disease, it is not always possible to carry them out in full, especially
6 INSTRUCTOR'S MANUAL FOR BROCK BIOLOGY OF MICROORGANISMS, 16e Copyright © 2021 Pearson Education, Inc. Copyright © 2021 Pearson Education, Inc. CHAPTER 1 The Microbial World 7
mynursytest.store mynursytest.store
ACCESS Test Bank for Brock Biology of Microorganisms 16th Edition
Madigan
CHAPTER
The Microbial World
1
elstb.netlify.app
PRINTED PDF | ORIGINAL DIRECTLY FROM THE PUBLISHER | 100% Summary
VERIFIED ANSWERS | DOWNLOAD IMMEDIATELY AFTER THE ORDER Chapter 1 introduces the study of microbiology for students, most of whom will
have had little or no exposure to the subject. Consequently, you have a good
opportunity to provide an overview of microbiology that demonstrates the
A+
important roles microorganisms (or microbes) play in human activities and in the
ecology of the entire biosphere. The ability of microorganisms to exist
independently in nature as free-living cells within larger microbial communities
(Figure 1.1) confers enormous adaptive advantages over cells of macroorganisms,
which are incapable of an independent existence.
BROCK BIOLOGY ОР
MICROORGANISMS 1.1 | Microorganisms, Tiny Titans of the Earth
Describe to students ways in which microbiology serves as both a basic and an applied
biological science. From a basic perspective, the study of microorganisms in laboratory
culture has been the primary means by which the fundamental genetic and biochemical
MADIGAN BENDER BUCKLEY SATTLEY STAHL properties of living cells have been revealed. From an applied perspective, microorganisms
directly affect the quality of human life in both detrimental and beneficial ways. Although
microorganisms are the causative agents of some of the most important human, animal, and
plant diseases, they are also used for the industrial production of antibiotics,
SOLUTIONS
pharmaceuticals, and foods. Microbes are also increasingly being used for beneficial
purposes as diverse as bioremediation of polluted sites, gene therapies for genetic diseases,
and the production of biofuels. Microbiology is therefore a science of far-reaching scope,
with applications that affect the quality of human life in a variety of ways (Figure 1.2).
MYNURSYTEST.STORE You should also emphasize to students the importance of microorganisms in the
emergence and maintenance of higher forms of life. From the production of molecular
oxygen (by cyanobacteria) to the biogeochemical cycling of key elements, such as carbon,
nitrogen, and sulfur, microorganisms play a major role in sustaining all life on the planet.
Point out in your course introduction that for all the reasons summarized in this section,
microbiology is the foundation of all biological sciences.
1.2 | Structure and Activities of Microbial Cells
Because microorganisms generally exist as free-living cells, it is important to discuss the
characteristics of cells in general. Emphasize that all cells exhibit a nonrandom organization with a
?
semipermeable membrane boundary that encompasses an internal system that is not in equilibrium
with its environment. Point out that prokaryotic cells (i.e., all Bacteria and Archaea) do not contain
membrane-bound, internal organelles as traditionally described for eukaryotic cells (the Eukarya;
Figure 1.4). In particular, the organization of prokaryotic DNA as a single chromosome in an
Complete Test bank, All Chapters
Copyright © 2021 Pearson Education, Inc. CHAPTER 1 The Microbial World 1
are included.
mynursytest.store
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,ACCESS Test Bank for Brock Biology of Microorganisms 16th Edition ACCESS Test Bank for Brock Biology of Microorganisms 16th Edition
Madigan Madigan
arrangement called a nucleoid, an aggregated mass of genetic material within the cytoplasm, is in slower growing diploid cells. This allows for greater adaptive potential through rapid selection
stark contrast to the compartmentalized, multichromosomal configuration typically found in for advantageous mutations and counterselection against deleterious mutations.
eukaryotes. However, despite the structural and morphological similarities of Bacteria and Archaea, The theoretical lower limit of size for a living cell is likely near 0.2 μm in diameter. This limit
make sure your students are aware early on that these groups of microorganisms have quite distinct
is dictated by the amount of volume required to contain cellular components that are crucial
evolutionary lineages and are, therefore, not closely related on a genetic level. This concept is
for maintaining life, such as (1) the presence of essential genes on the chromosome; (2)
discussed in more detail in Section 1.5.
having a sufficient number of ribosomes; and (3) containing a minimal number of metabolic,
The ability of cells to maintain a thermodynamic energy flow far from equilibrium
structural, and transport proteins within the cell. Challenge students to list these and other
defines what we refer to as a living system. All living systems display some form of
molecular components that a cell would have to contain to maintain life. Remind students
enzyme-driven metabolism in which both energy-yielding (catabolic) and energy-
consuming (anabolic) biochemical reactions are catalyzed concurrently. These chemical that some cells are parasitic in nature. Inform them that, much like viruses, such
transformations allow for biosynthesis of new cell structures and, ultimately, cell division microorganisms often have streamlined genomes that lack important genes and may make
(microbial growth). Figure 1.5 shows the characteristics that define cellular life, some of them dependent upon their hosts for growth. Can such organisms truly be considered living?
which are universal (e.g., metabolism and evolution) and some of which occur only in This might make a good outside project for group debate, requiring students to view the cell
some cells (e.g., differentiation and motility). as a three-dimensional physical structure constrained in space and to research a problem
that is currently being debated.
1.3 | Cell Size and Morphology Using Figure 1.8, point out the three major morphologies of prokaryotic cells (coccus, rod, and
spirillum). Inform your students that, in some species, the cells remain attached following cell
The presentation in the text of the significance of being small is an important concept for students division, giving rise to different arrangements that are often genus-specific. For example, coccus
to internalize as they begin their study of microbiology. Table 1.1 shows the wide size range cells may exist as long chains (Streptococcus) or grapelike clusters (Staphylococcus). Less
variability of bacterial cells, which range from a diameter of about 0.2 µm to over 700 µm. Use the common cell morphologies also exist, such as spirochetes, appendaged (budding) bacteria, and
two examples of unusually large bacteria discussed in this section to illustrate the current upper filamentous bacteria (Figure 1.8). Stress to students that these morphologies are only representative
limit of bacterial cell size: (1) the surgeonfish gut symbiont Epulopiscium fishelsoni (>600 µm in of those found in nature. Other unusual shapes have also been described in rare cases (e.g., square-
length; Figure 1.6a), and (2) the sulfur chemolithotroph Thiomargarita namibiensis (750 µm; and star-shaped cells!).
Figure 1.6b). The evolutionary “rationale” for the existence of unusually large-celled bacteria is a Before the molecular era, morphological and physiological properties were used to classify
mystery when one considers that the metabolic rate of a cell varies inversely with the square of its bacterial species. However, we now know that these criteria are poor predictors of evolutionary
size. Ask your students for ideas and/or hypotheses that might explain the selective advantage of relationships. For example, certain species of Archaea may appear identical in size and shape to
large cell size in these two prokaryotes. species of Bacteria under the microscope, but these organisms are of different phylogenetic
The fact that bacteria can live independently as single cells (unlike an individual cell of a domains and thus are not closely related to one another on an evolutionary basis. The cell
multicellular organism) suggests that they must possess some capabilities that provide a selective morphology of a particular species is primarily a result of selective pressures in a given habitat that
advantage over their multicellular counterparts that ensure their survival on the planet. Small cells favored a particular cell shape for enhanced reproductive success.
have more surface area to volume (i.e., a higher surface-to-volume ratio), and this alone confers
many of the evolutionary advantages of being small, including the following: 1.4 | An Introduction to Microbial Life
● Rapid nutrient and waste transport into and out of the cell allows for faster metabolic rates and
growth rates. This section of the chapter provides an overview of the key factors that distinguish cells of the
● Rapid growth rates result in the rapid production of large populations of cells. These different domains of life, and how these are further distinguished from acellular microbes—the
populations, in turn, can greatly affect the physiochemical conditions of an ecosystem within a viruses. Figure 1.9 beautifully compares the size relationships of a variety of microbial forms and
short time period. components, from the uncommonly large bacterium Epulopiscium fishelsoni at a length of 600 μm
● Transport rates are a function of the surface area of the cytoplasmic membrane relative to cell (see also Figure 1.6) to individual proteins at the limit of resolution of an electron microscope
volume. Use Figure 1.7 to mathematically demonstrate to students that the surface area of a (0.2 nm). Mention the following key points:
sphere is a function of the square of the radius, whereas the volume of a sphere is a function of the ● The greatest diversity of Bacteria and Archaea has never been cultured in the laboratory, and
cube of the radius. This means that the surface-to-volume ratio of a spherical cell can be such species are known only by their DNA sequences found in environmental samples.
expressed as 3/r, where r equals the radius of the cell. Therefore, a coccus cell having a smaller ● Although they both have a prokaryotic cell structure, Bacteria and Archaea are not closely
radius has more surface area per volume and, thus, more efficient transport capabilities, than a related. On a molecular level, Archaea have much in common with the eukaryotes.
coccus cell having a larger radius. ● The metabolic and physiological diversity of microorganisms, especially the Bacteria and
● Rates of evolutionary change are higher in smaller, faster growing haploid cells than in larger, Archaea, is astonishing, with species capable of aerobic respiration, anaerobic respiration,
2 INSTRUCTOR'S MANUAL FOR BROCK BIOLOGY OF MICROORGANISMS, 16e Copyright © 2021 Pearson Education, Inc. Copyright © 2021 Pearson Education, Inc. CHAPTER 1 The Microbial World 3
mynursytest.store mynursytest.store
,ACCESS Test Bank for Brock Biology of Microorganisms 16th Edition ACCESS Test Bank for Brock Biology of Microorganisms 16th Edition
Madigan Madigan
fermentation, and/or phototrophy inhabiting nearly every imaginable habitat on Earth. microorganisms “simple,” insignificant creatures that only cause disease—and will set the
● Microorganisms of the domain Eukarya include the fungi, protists (including the protozoa and stage for more detailed study in future chapters.
algae), and helminths (roundworms and flatworms). Finally, point out that microorganisms can be found in even the most inhospitable
environments by human standards. Students are often amazed at the extreme conditions in
● The Eukarya lineage is evolutionarily younger than either the Bacteria or the Archaea.
which microorganisms can thrive (Table 1.2). Point out that even in punishingly harsh
● Because viruses are acellular and incapable of autonomous reproduction, most microbiologists ecosystems, such as in volcanic hot springs or freezing Antarctic lakes, microbes called
consider them to be nonliving biological entities. extremophiles are able to exist or even thrive in conditions that define the physiochemical
● Viral genomes may be either DNA or RNA, but not both. Whether DNA or RNA, their limits to life on Earth. These communities contain a reservoir of genetic diversity that is
genomes may be single- or double-stranded. All cells have double-stranded DNA genomes. largely unexplored and that could benefit humankind in as yet unknown ways.
● Viruses also display incredible diversity, despite the fact that they are nonliving, with broad
host ranges. Viruses are known to infect cells from all three domains of life. 1.6 | The Impact of Microorganisms on Human Society
Students probably understand the importance of microorganisms as agents of infectious disease,
1.5 | Microorganisms and the Biosphere and indeed, this has been a driving force in the development of microbiology as a distinct
scientific discipline. The effects of microorganisms upon human affairs have been remarkable,
Although Earth is believed to be about 4.6 billion years old, several lines of evidence particularly when one compares the foremost causes of death in the United States at the
indicate that the appearance of multicellular life did not occur until about 600 million years beginning of the twentieth century (before the widespread use of antibiotics and vaccines) with
ago (Figure 1.10). By contrast, microbial cells (single-celled prokaryotes) likely appeared the major causes of death in this century (Figure 1.13). While the deleterious effects of
between 3.8 and 3.9 billion years ago and therefore were the only inhabitants of the planet pathogenic bacteria to human wellness should be discussed here, it is important to also stress the
for about 80% of its history! The appearance of multicellular life was necessarily preceded key beneficial roles microorganisms play in agriculture (Figure 1.14), in human digestive health
by the accumulation of significant amounts of molecular oxygen (O2) in the atmosphere, a (Figure 1.15), in the food and beverage industries (Figure 1.16), and in the growing fields of
phenomenon that resulted from the activity of cyanobacteria and the evolution of a biotechnology and alternative and renewable energy (Figure 1.17). With this discussion, students
chlorophyll molecule that could use water (H2O) as electron donor (see Chapter 13). should become aware of the tremendous influence of microorganisms in human society.
Develop this concept for students in some detail at an early stage in the course to provide The genomes of microorganisms hold incredible potential for the production of useful and
proper historical perspective of important events in cellular evolution. You may wish to valuable products. The traditional methods of employing microorganisms for human use (e.g.,
start with the evidence supporting the hypothesis that the first self-replicating “entities” fermentation) have evolved into the large-scale, commercial ventures of industrial microbiology
may have been RNA molecules, and the incorporation of these entities within lipid and biotechnology. Whereas industrial microbiology exploits microbial activities in the
membranes may have represented the first cell type(s). This topic will be more thoroughly production of large quantities of lower cost commodities, such as solvents and enzymes, the
discussed in Chapter 13. “biotech” industry uses genetically engineered microorganisms to produce smaller quantities of
Discuss with your students some of the events that led to multicellular forms of life. The specialized products of high value, such as certain pharmaceuticals. An excellent example is the
evolution of anaerobic phototrophic metabolisms likely began within 500 million years production of human insulin by Escherichia coli, an innovation that made the treatment of
after the appearance of the first cells, followed nearly a billion years later by the evolution
diabetes affordable for people from all economic backgrounds. In addition to producing a product
of cyanobacteria from these early phototrophs (Figure 1.11), thus starting the slow process
directly, bacterial cells can be used as a vehicle to introduce specific genes into the genomes of
of oxygenating the atmosphere and the evolutionary path to multicellularity.
other organisms for commercial production of a desired product. For example, genetic
Impress upon your students the enormous abundance of microorganisms in the
engineering of Agrobacterium tumefaciens, a plant pathogen that naturally transfers DNA
biosphere; the total number of microbial cells on Earth is estimated to be about eight orders
directly into plant cells upon infection, has led to the use of plants for the production of human
of magnitude greater than the number of stars in the universe! Emphasize that this vast
antibodies that have potential anticancer or antiviral properties.
quantity of microbial biomass sequesters more life-sustaining nutrients (e.g., carbon,
One area of extensive research in industrial microbiology is the production of biofuels. These
nitrogen, and phosphorus) than all plants and animals combined (Figure 1.12).
products are often used to supplement petroleum-based fuels and may include methane, ethanol,
Introduce the students to microbial ecology, the exciting subdiscipline of microbiology
biodiesel, hydrogen (H2), and other fuels derived from microbial metabolisms. Microorganisms
that focuses on the interactions and influence of microbial communities on the macroscopic
are also being used extensively to restore polluted natural areas in a process called
world around them. The biochemical conversions and molecular interactions of
bioremediation. By applying specific microorganisms (or nutrients to stimulate their growth) to
microorganisms significantly control the balance and community structure of all living
polluted sites, contaminants such as pesticides, heavy metals, and crude oil and other
organisms in an ecosystem. In fact, the very existence of multicellular life depends upon
hydrocarbons can all be cleaned successfully and thoroughly.
the nutrient cycling activities of microorganisms. The effect of microbes on animals,
plants, and global ecosystems is a topic interwoven throughout a number of chapters in the
text. These concepts will come as a surprise for most students—who generally consider
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1.7–1.10 | Microscopy and the Origins of Microbiology 1.11 | Pasteur and Spontaneous Generation
It is important to emphasize the historical roots of microbiology, particularly considering its As a young researcher, Louis Pasteur was formally trained as a chemist with expertise in the
rather recent beginnings as a systematic field of science in the nineteenth century and the fact field of crystallography. His knowledge of the optical properties of crystals provided the
that several new fields have arisen from this discipline (e.g., molecular biology and basis for his early investigations into the biological sciences. Begin the discussion of his
biotechnology). Lead the students on a chronological journey, beginning with Robert celebrated scientific achievements by pointing out that it was his observation that living
Hooke’s first description of a microorganism (a fungal mold) in 1665 (Figure 1.18) and organisms discriminate between optical isomers of metabolites during growth (Figure 1.30)
Antoni van Leeuwenhoek’s microscope and publication of the first observation of bacteria in that led him to begin a series of experiments that would result in the defeat of the centuries-
1684 (Figure 1.19). old theory of spontaneous generation. Pasteur’s experimental design that finally disproved
Following your introduction of the pioneers of microscopy, provide the students with an this theory introduced the now famous swan-necked flask (Figure 1.31). His work is a
overview of microscopic methods in common usage today. The variety of methods available classic example of the effectiveness of using the scientific method and controlled
for observing microorganisms must be introduced early, as much of the presentation of experimentation to resolve questions rather than personal observation and interpretation,
structure–function relationships depends upon the excellent micrographs that appear throughout which often lead to unsubstantiated (and often erroneous) conclusions. Point out to students
the book. Although details of microscopy are more easily introduced in the laboratory portion that disproving spontaneous generation resulted in the development of effective procedures
of the course, the material included here is pertinent to effective lecture presentation. for controlling microbial growth, including the familiar process of pasteurization. Outline
● Discuss the basic principles and components of the compound light microscope, the major career accomplishments of Pasteur, pointing out the fact that although his
including the relationships between resolution and magnification, and numerical professional training pertained to chemistry rather than biology, his laboratory
aperture (Figure 1.20). Note that although bright-field microscopy is fine for visualizing experimentation led him to the study of microorganisms.
pigmented cells (Figure 1.21), it is not an efficient tool for viewing unstained cells with ● As a chemist, Pasteur’s work with optical isomers of amyl alcohol, a byproduct of
no natural pigmentation, such as nonphototrophic bacteria. alcohol fermentation by beets, led him to confirm that fermentation was not a strictly
● This deficiency will lead to a discussion of various methods employed to increase chemical phenomenon but that living yeast cells were required for the process. The
contrast. Discuss the various simple dyes used to stain cells, most of which are outcome of his fermentation studies led him to the classic experiments that defeated
positively charged, basic dyes capable of binding to negatively charged cell surfaces spontaneous generation (Figure 1.31).
(e.g., methylene blue and crystal violet; Figure 1.22). Continue the discussion of ● Discuss the many other accomplishments of Pasteur, including the development of
differential stains, the most widely used of which is the Gram stain (Figure 1.23). vaccines for anthrax, fowl cholera, and rabies. The dramatic results of his rabies
● Students should understand that while staining procedures increase the contrast of cells vaccine, which saved a young boy, startled the scientific world and led the French
against the background to make them more visible, they also kill cells and may distort government to build the Pasteur Institute in Paris in 1888 (Figure 1.32). Together with
their appearance. Discuss phase-contrast microscopy and dark-field microscopy (Figure Robert Koch, whose scientific achievements are discussed next, Pasteur played a major
1.24), two tools that allow one to look at living cells without the need for staining. role in establishing the field of medical microbiology.
● Fluorescence microscopy is widely used in clinical diagnostic microbiology and
environmental microbiology (Figure 1.25). Most students who enter the biotechnology 1.12 | Koch, Infectious Diseases, and Pure Cultures
industry or medical profession will work with fluorescent molecules (such as those used
for fluorescence antibody staining methods). The variety and sensitivity of these Explain to your students that for centuries many thought that some unknown agent from a diseased
molecules have increased dramatically over the past decade. This has allowed the person could be transmitted to healthy people, but no real proof of this existed until the work of
development of a wide variety of nonradioactive alternatives to biological assays that Robert Koch (Figure 1.33). Although Koch was 21 years younger than Pasteur, several of their
are now routinely used in research. greatest achievements were carried out around the same time during the late 1800s. The following
● Students should be interested in the micrographs from three-dimensional imaging of list serves as an introduction to the works of Koch for your students.
cells. Depending upon the level of the course, you may choose to discuss the principles ● Koch’s work on the germ theory of disease (1876) was perhaps the most important stimulus
of differential interference contrast microscopy (Figure 1.26) and confocal scanning for the development of medical microbiology. Given the focus on bioterrorism in recent
laser microscopy (Figure 1.27). Lastly, show and discuss the micrographs obtained from years, students may find it interesting that Koch’s work leading to this important theory
electron microscopy (Figures 1.28 and 1.29). Note the differences between scanning involved the study of the endospore-forming bacterium Bacillus anthracis, the causative
electron microscopy (SEM), which provides an image of the external features of a agent of anthrax. Carefully discuss Koch’s postulates, the use of which has since led to
specimen, and transmission electron microscopy (TEM), in which thin sections of the discoveries for the prevention and cure of many infectious diseases (Figure 1.33). However,
specimen show its detailed internal structure. be sure to note that while Koch’s postulates are the “gold standard” for determining the
causative agent of a disease, it is not always possible to carry them out in full, especially
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