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Chapter 13: Evolution and Diversity
Among the Microbes
Bacteria, archaea, protists, and viruses: the
unseen world
Lectures by Mark Manteuffel, St. Louis Community College
Learning Objectives
 Know
there are microbes in all three
domains
 Know
that bacteria may be the most
diverse of all organisms
 Describe
how, in humans, bacteria can
have harmful or beneficial health effects
Learning Objectives
 Discuss
how Archaea exploit some of the
most extreme habitats
 Describe
 Discuss
the protists
how viruses are at the border
between living and non-living
13.1–13.2
There are
microbes in
all three
domains.
13.1 Microbes are the simplest
but most successful organisms on
earth.
How can a microbe function when
its body is just a single cell?
Amoeba as an example
How would you decide whether a
group of organisms can be
considered successful?
Microbes Are Genetically Diverse
 >500,000
 Millions
kinds
more expected to be distinguished!
Microbes Can Live Almost Anywhere
and Eat Almost Anything
Microbes
are
abundant!
Take-home message 13.1
 Microbes
are simple, but they do
everything that multicellular organisms do.
 They
can live anywhere, from moderate to
extreme environments.
 There
are millions of different kinds of
microbes on earth, in enormous numbers.
13.2 Not all microbes are
evolutionarily related.
Take-home message 13.2
 Microbes
are grouped together only
because they are small, not because of
evolutionary relatedness.
 They
occur in all three domains of life, and
also include the viruses, which are not
included in any of the domains.
13.3−13.5
Bacteria
may be the
most
diverse of all
organisms.
13.3 What are bacteria?
Take-home message 13.3
 Bacteria
are efficient single-celled
organisms, with an envelope surrounding
the cytoplasm, which contains the DNA
(they have no nuclei and no intracellular
organelles).
 Bacterial
cells undergo binary fission, and
a single cell can grow into a colony of
cells.
13.4 Bacterial growth and
reproduction is fast and
efficient.
Bacteria Carry Genetic Information
in Two Structures
1. A circular DNA molecule called the
chromosome (1 or more)
2. Circular DNA molecules called plasmids
• metabolic plasmids
• resistance plasmids
• virulence plasmids
Would it be useful to be able to
transfer genetic information from one
adult human to another?
Take-home message 13.4
 Bacteria
 They
grow rapidly.
have efficiently organized
chromosomes—genes are organized in
groups with related functions and virtually
all the DNA codes for proteins.
Take-home message 13.4
 Bacteria
sometimes carry the genes for
specialized traits on small DNA molecules
called plasmids that can be transferred
from one bacterial cell to another by
conjugation.
 DNA
can also be transferred laterally
between bacterial cells by transduction or
transformation.
13.5 Metabolic diversity among
the bacteria is extreme.
Photoautotrophs and the Oxygen
Revolution
Take-home message 13.5
 Some
bacteria eat organic molecules,
some eat minerals, and still other bacteria
carry out photosynthesis.
 About
2.6 billion years ago, the
photosynthesizing bacteria were
responsible for the first appearance of free
oxygen in the Earth's atmosphere.
13.6–13.9
In humans,
bacteria can have
harmful or
beneficial
health effects.
13.6 Many bacteria are beneficial
You owe your life to bacteria?
• Normal flora
• Probiotic therapy
Take-home message 13.6
 Your
body fights bacteria with bacteria.
A
disease-causing bacterium must colonize
your body before it can make you sick,
and your body is already covered with
harmless bacteria.
 If
the population of harmless bacteria is
dense enough, it will prevent invading
bacteria from gaining a foothold.
13.7 Bacteria cause many
human diseases.
Pathogenic bacteria
Take-home message 13.7
 Some
bacteria always cause disease and
others do no harm except under certain
conditions.
example, Streptococcus pyogenes can
be harmless, but under some conditions it
releases toxins that are responsible for
strep throat, scarlet fever, and necrotizing
fasciitis (caused by the flesh-eating
strains).
 For
13.8 Bacteria’s resistance to
drugs can evolve quickly.
Where do antibiotics come from, and
why do they so quickly lose their
effectiveness?
Chemicals that kill!
Bacteria and other microbes resist
antibiotics in a variety of ways:
 Pumping
 Proteins
antibiotics out of their cell
that bind to the antibiotic
molecule and block its lethal effect
Bacteria and other microbes resist
antibiotics in a variety of ways:
 Enzymes
that break down the antibiotic
molecules that are then used as fuel to
help the bacteria grow faster
Why is it essential to take every
dose of an antibiotic prescribed
by a doctor?
Take-home message 13.8
 Microbes
routinely evolve resistance to
antibiotics.
 The
genes that allow bacteria to combat
antibiotics are located on plasmids, and
plasmid transfer allows an antibioticresistant bacterium to pass that resistance
to other bacteria.
Take-home message 13.8
 Excessive
use of antibiotics in medicine
and agriculture has made several
pathogenic bacteria resistant to every
known antibiotic, and infections caused by
these bacteria are nearly impossible to
treat.
13.10 Archaea are profoundly different
from bacteria.
Additional Differences among Bacteria,
Archaea, and Eukarya
 Chemical
compositions of the plasma
membranes, cell walls, and the flagellae
 Eukarya
have a distinct cell nucleus and a
nuclear membrane; bacteria and archaea
do not.
Take-home message 13.10
 Archaea
show a set of characteristics that
places them between bacteria and
eukaryotes on the tree of life.
Take-home message 13.10
 Archaea
and bacteria may look similar, but
they have large and significant differences
in their DNA sequences, as well as
differences in their plasma membranes,
cell walls, and flagella.
 Furthermore,
neither archaea nor bacteria
resemble eukarya in one key way: only
eukarya have a distinct cell nucleus and
nuclear membrane.
13.11 Archaea thrive in habitats
too extreme for most other
organisms.
Extremophiles
Take-home message 13.11
 Archaeans
can tolerate extreme physical
and chemical conditions that are
impossible for most other living
organisms, but they also live in moderate
conditions and even in the human
intestine.
13.12 Much Archaean diversity
has yet to be discovered.
Important applications in
bioengineering and
environmental remediation
Remember Thermus aquaticus?
Enormous Potential for Industries:
Bioremediation
 Degrade
hydrocarbon
 Clearing mineral deposits from pipes in
the cooling systems of power plants
Take-home message 13.12
 Archaea
are hard to study because many
require extreme heat or pressure to grow,
and these conditions are not easy to
provide in a laboratory.
 But
the ability of archaea to grow in such
extreme conditions makes them
potentially valuable for industrial and
environmental purposes.
13.14 There are animal-like
protists, fungus-like protists, and
plant-like protists.
13.16–13.19
Viruses are at
the border
between
living and
non-living.
13.16 Viruses are not exactly
living organisms.
Lytic Cycle
Lytic Cycle video
Lysogenic Cycle
Lytic and Lysogenic
Take-home message 13.16
A
virus is not alive, but it can carry out
some of the same functions as living
organisms, provided that it can get inside
a cell.
Take-home message 13.16
A
virus takes over the protein-making
machinery of the host cell to produce
more viral genetic material (RNA or DNA)
and more viral protein.
 The
viral proteins and genetic material are
assembled into new virus particles and
released from the cell.
13.17 Viruses are responsible for
many health problems.
Why do flu viruses change quickly?
DNA vs. RNA viruses
Take-home message 13.17
 Many
 DNA
diseases are caused by viruses.
viruses are relatively stable because
DNA replication enzymes check for errors
and correct them during replication.
Take-home message 13.17
 RNA
viruses change quickly because RNA
replication enzymes do not have errorchecking mechanisms.
13.18 Viruses infect a wide
range of organisms.
What role does a pig play in the
transmission of virus from a bird
to a human?
Bird Flu
 So
far requires close contact with infected
flocks of birds or by eating birds that had
died of the virus.
 WHO
and national health agencies are
preparing for a worldwide pandemic.
Mixing RNA
 Pig
+ bird flu virus + human virus = might
produce a new form of the virus that
carries the genes that make the bird flu
lethal to humans AND the gene that codes
for the host-entry glycoprotein.
Take-home message 13.18
 Glycoproteins
on the surfaces of viruses
determine what cells they can invade.
 Most
viruses infect just one species, or
only a few closely related species, and
enter only one kind of cell in that species.
13.19 HIV illustrates the
difficulty of controlling
infectious viruses.
HIV mutates easily.
HIV Attacks White Blood Cells
The Immune System Collapses
 Normally
white blood cells all work
together to identify and destroy cells that
have been infected by a virus.
 HIV
kills the cells that hunt for viruses and
bacteria.
 The
immune system begins to fail.
Take-home message 13.19
 HIV
is especially difficult to control.
 Mutations
change the properties of the
virus so that it is hard for the immune
system to recognize it, and they produce
variants that are resistant to the drugs
being used to treat the HIV infection.