1. Chapter 16
Evolution of
Microbial Life
Lecture Outline
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2. 16.1 Viruses have a simple structure
 Viruses are noncellular /nonliving
 Size comparable to large protein macromolecule
 Ranging from 0.2 to 2 μm
 Basic anatomy of a Virus
 Outer capsid composed of protein
 May be surrounded by outer membranous envelope
 Inner core of nucleic acid (DNA or RNA)
16-2

3. Figure 16.1A Adenovirus, a naked virus, with a polyhedral capsid and
a fiber at each corner
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
capsid
fiber
DNA
protein unit
TEM 80,000×
(Right): © Dr. Hans Gelderblom/Visuals Unlimited 16-3

4. Figure 16.1B Influenza virus, surrounded by an envelope with spikes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
spike RNA
envelope
capsid
20 nm
(Right): © K.G. Murti/Visuals Unlimited
16-4

5.  Classification of Viruses:
1. Their type of nucleic acid – DNA or RNA
2. Whether nucleic acid is single-stranded or
double-stranded
3. Size and shape
4. Presence or absence of an outer membrane
16-5

6. 16.2 Some viruses reproduce inside bacteria
 Bacteriophages (phages)
 Viruses that infect bacteria
 Two types of life cycles
 Lytic cycle
 Most common
 5 stages
 Lysogenic cycle
 Phage becomes latent – called prophage
 Environmental factors trigger entry into lytic cycle
16-6

7. Figure 16.2 The lytic and lysogenic cycles in prokaryotes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1 ATTACHMENT
Capsid combines with receptor.
bacterial nucleic acid
cell wall
bacterial capsid
DNA
5 RELEASE 2a PENETRATION 2b INTEGRATION Viral DNA is
New viruses leave host cell. Viral DNA enters host. integrated into bacterial DNA
and then is passed on when
bacteria reproduce.
LYTIC viral
CYCLE DNA
viral
DNA
LYSOGENIC
CYCLE
4 MATURATION 3 BIOSYNTHESIS
Viral components are assembled. Viral components are synthesized.
capsid prophage
viral
DNA
daughter cells 16-7

8. 16.3 Plant diseases caused by Viruses
 Most plant viruses are RNA viruses
 Generalized symptoms
 Stunted growth; discoloration of leaves, flowers, and fruits; death
of stems, leaves, and fruits; irregularities in fruit size; etc.
 Viruses seldom kill their plant hosts
 Spread by variety of mechanisms
16-8

9. Figure 16.3A The tobacco mosaic virus (TMV) is responsible for
discoloration in the leaves of tobacco plants
16-9

10. Figure 16.3B A virus is
responsible for the
variegation and
streaking in Rembrandt
tulips
 Viruses used
intentionally to
produce
streaking
 Weakens plant
and it does not
live long
16-10

11. HOW BIOLOGY IMPACTS OUR LIVES
16A Humans Suffer from Emergent Viral
Diseases
 Emergent diseases – newly recognized as infectious
 Viruses are constantly in a state of evolutionary flux
 Can acquire new spikes to allow entry into new cells
 Virus that cannot pass from human to human after
jumping from an animal host will not be capable of
causing an epidemic
 A large-scale infection of many persons
 Some emergent diseases are transmitted by vectors
 Mosquitoes used by several viral diseases
16-11

12. HOW BIOLOGY IMPACTS OUR LIVES
16A Humans Suffer from
Emergent Viral Diseases
 H1N1 virus
 Usually found in pigs, in humans it causes the symptoms of flu
 Named after spikes H1 and N1
 Severe acute respiratory syndrome (SARS)
 Causes high fever, body aches, and pneumonia
 Avian influenza (or bird flu)
 Disease does not often spread from chickens to humans, nor is
it efficiently transmitted among humans
 Ebola
 1 of a number of viruses that cause hemorrhagic fever
 Highly contagious and fatal
 Vector and animal reservoir unknown
16-12

13. 16.4 Viruses reproduce inside animal cells and
cause diseases
 Life cycle of a DNA virus in animals and humans
 Attachment: Glycoprotein spikes projecting through
the envelope allow the virus to bind to host cells
 Penetration: After the viral particle enters the host
cell, uncoating follows and viral DNA enters the host
 Biosynthesis: The capsid and other proteins are
synthesized by host cell ribosomes according to viral
DNA instructions
 Maturation: Viral proteins and DNA replicates are
assembled to form new viral particles
 Release: In an enveloped virus, budding occurs and
the virus develops its envelope
16-13

14. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1 Attachment: Spike
Figure 16.4
combines with receptor.
capsid Replication of an
animal virus
2 Penetration: Virus
enters cell, and
uncoating occurs.
envelope
uncoating
spike
Cytoplasm
nucleic
viral DNA
acid (DNA)
nuclear
plasma
pore
membrane
3a Biosynthesis: Viral
proteins are synthesized.
Nucleus
ribosome
viral mRNA
capsid
protein
3b Biosynthesis: ER
Many strands of
DNA are produced. 16-14

15. Figure 16.4
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
capsid Replication of an
animal virus
(Cont.)
viral spikes
4 Maturation: Viral
components are
assembled.
5 Release: Budding gives
virus an envelope.
16-15

16. 16-16

17. 16.5 HIV (the AIDS virus) is a retroviruses
 Genome consists of RNA, instead of DNA
 Retrovirus
 Uses reverse transcription from RNA into DNA in order to insert
a complementary copy of its genome into the host’s genome
 Uses reverse transcriptase enzyme
 HIV provirus
 Viral DNA integrated into host DNA.
 Usually transmitted to another person by means of cells that
contain proviruses
 Emergent viral disease that jumped from chimpanzees to
humans
16-17

18. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 16.5
Reproduction
1 of HIV
Attachment
receptor
envelope
spike
2
Penetration
capsid
nuclear
3 pore
Reverse transcription
viral RNA
reverse transcriptase
cDNA
4
Replication Integration
host
ribosome DNA
5
Biosynthesis viral
mRNA provirus
viral
ER enzyme 16-18

19. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Replication
4
Integration
Figure 16.5
host
Reproduction
of HIV (Cont.)
ribosome DNA
5
Biosynthesis viral
mRNA provirus
viral
ER enzyme
capsid
protein
6
spike Maturation
viral RNA
7
Release
16-19

20. Prions
 Prions
 Protein infectious particles
 Misfolded proteins whose presence causes other
proteins to also become misfolded
 Cause rare but serious brain diseases, such as
Creutzfeldt-Jakob Disease (CJD)
16-20

21. Figure 16B.1 A virus is less complex than a prokaryote, because all it takes is a
capsid surrounding a genetic material. Like this one, some viruses use RNA as
their genetic material
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
protein unit
RNA
caspid
16-21

22. Figure 16B.2 A prokaryote is more complex, both metabolically and structurally,
than a virus. Like this one, prokaryotes always use DNA as their genetic material
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
ribosomes
DNA
plasma enzymatic
membrane proteins
cellwall
phospholipid
bilayer
16-22

23. Figure 16.6B Chemical evolution at hydrothermal vents
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
plume of hot water
rich in iron sulfides
hydrothermal
vent
© Ralph White/Corbis
16-23

24. 16.9 Prokaryotes have unique structural
features
 Bacteria & Archaea are in separate domains due
to molecular and cellular differences
 Unicellular organisms / Prokaryotic
 Lack a eukaryotic nucleus and membranous
organelles
 Nucleoid – dense area with a single chromosome
 May have plasmids – accessory rings of DNA
 Cell wall strengthened by peptidoglycan
 May have capsule or slime layer
16-24

25. 16.9 Prokaryotes have unique structural
features
 Appendages:
 Pili – short, for attachment
 Flagella – longer, for movement
 Three Basic Shapes of Prokaryotes
 Cocci (sing., coccus) – round or spherical
 Bacilli (sing., bacillus) – rod-shaped
 Spirilla (sing., spirillum) – spiral- or helical-shaped
16-25

26. Figure 16.9A
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Anatomy of
bacterium
flagella
pili
ribosome
1 µm
nucleoid
plasma membrane
cell wall
capsule
(bacterium, whole): © Ralph A. Slepecky/Visuals Unlimited; (bacterium, circle): Courtesy Harley W. Moon, U.S. Dept. of Agriculture
16-26

27. Figure 16.9B The three shapes of bacteria
16-27

28. 16.10 Prokaryotes reproduce by binary fission
 Reproduce asexually using binary fission
 Results in two prokaryotes of equal size
 Genetically identical (but higher mutation rate)
 Not mitosis
 Three steps:
 1. DNA replication
 2. Chromosome segregation
 3. Cytokinesis
16-28

29. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1 DNA replication
Figure 16.10 Binary
fission results in two
bacteria
2 Chromosome segregation
3 Cytokinesis
Daughter cells 16-29

30. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
cytoplasm
cell wall
nucleoid
Cytokinesis
0.5 µm
© CNRI/SPL/Photo Researchers, Inc.
Figure 16.10 Binary fission results in two bacteria (Cont.)
16-30

31. Some bacteria form Endospores
 When faced with unfavorable environmental
conditions, some bacteria form endospores
 A portion of the cytoplasm and a copy of the chromosome
dehydrate and are then encased by a heavy, protective
spore coat
 Spores survive in the harshest of environments and
for very long periods of time
 Not a means of reproduction
16-31

32. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
endospore
endospore within
Clostridium tetani.
© Alfred Pasieka/SPL/Photo Researchers, Inc.
16-32

33. 16.11 Gene are transfer between bacteria
1. Transformation
 Recipient picks up “free DNA” from its surroundings
1. Conjugation
 Donor bacterium passes DNA to the recipient by way
of a conjugation pilus
 Plasmid – small circle of DNA
1. Transduction
 Bacteriophages carry portions of bacterial DNA from
a donor cell to a recipient
16-33

34. Figure 16.11A
Gene transfer by
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
donor cell recipient cell
transformation
Lysis of DNA
donor cell
releases
DNA.
Donor DNA is
taken up by recipient.
16-34

35. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
donor cell recipient cell Figure 16.11B Gene
transfer by conjugation
donor cell
plasmid
DNA
Donor DNA is transferred directly to
recipient through a conjugation pilus.
16-35

36. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
donor cell recipient cell Figure 16.11C
Gene transfer
by transduction
Bacteriophage
infects a cell.
Donor DNA
is picked up by
bacteriophage
Donor DNA
transferred when bacteriophage
infects recipient. 16-36

37. Prokaryotes have various means of nutrition
 Obligate Anaerobes
 Unable to grow in the presence of free oxygen
 A few serious illnesses – such as botulism, gas
gangrene, and tetanus – are caused by anaerobic
bacteria
 Facultative anaerobes
 Able to grow in either presence or absence of oxygen
 Most prokaryotes are aerobic and require a
constant supply of oxygen
16-37

38.  Autotrophic Prokaryotes
 Produce their own organic nutrients / “self-feeding”
 Photoautotrophs
 Use solar energy to reduce carbon dioxide to organic
compounds
 Chemosynthetic
 Remove electrons from inorganic compounds use them to
reduce CO2 to an organic molecule
 Ex: Bacteria in a hydrothermal vent
16-38

39. Figure 16.12A Some anaerobic photosynthetic bacteria live in the
muddy bottoms of eutrophic lakes
16-39

40. Figure 16.12B Some chemosynthetic prokaryotes live at hydrothermal
vents Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
tubeworm
clam
© Science VU/Visuals Unlimited 16-40

41.  Heterotrophic Prokaryotes (“other feeding”)
 Take in organic nutrients
 Saprophytic bacteria
 Ex: Decomposers in soil
 Symbiosis: Two different species living
together.
 Mutualism – both species benefit
 Commensalism– one species benefits, no effect on
the other species.
 Parasitism – one species benefits, one is harmed.
16-41

42. 16.13 The cyanobacteria are ecologically
important organisms
 Pigments occur in the membrane of flattened
disks called thylakoids
 Perform photosynthesis like plants
 Believed to be responsible for introducing
oxygen into the atmosphere
 Some possess heterocysts for nitrogen fixation
 Common in water, soil, and moist surfaces
 Some are symbiotic with other organisms
(e.g. lichens are cyanobacteria and fungi)
16-42

43. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
DNA
thylakoids
cell wall
storage
granule
plasma
membrane
Oscillatoria cell
heterocyst
Gloeocapsa, a unicellular form Anabaena, a colonial form Oscillatoria, a filamentous form
(Gloeocapsa): © Runk/Schoenberger/Grant HeilmanPhotography; (Anabaena): © Philip Sze/Visuals Unlimited; (Oscillatoria): © Tom Adams/Visuals Unlimited
FIGURE 16.13 Diversity among the cyanobacteria 16-43

44. 16.14 Archaea live in extreme environments
 Structure and Function
 No peptidoglycan in cell wall
 Ex: Methanogens-produce methane from the
decomposition of organic matter
 Archaea are found in extreme environments
 Halophiles-organism that requires a salty environment
 Thermoacidophiles-environments are extremely
acidic with high temperatures 16-44

45. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Methanosarcina
mazei
(swamp): © altrendonature/Getty Images; (inset): © Ralph Robinson/Visuals Unlimited
Figure 16.14A Methanogen habitat and structure 16-45

46. Figure 16.14B Halophile habitat and structure
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Great SaltLake, Utah Halobacterium
salinarium
(Great Salt Lake): © John Sohlden/Visuals Unlimited; (inset): FromJ.T. Staley, et al., Bergey's Manual of Systematic Bacteriology, Vol. 13,
© 1989Williams and Wilkins Col, Baltimore. Prepared by A.L. Usted Photography by Dept. of Biophysics, Norwegian Institute of Technology
16-46

47. Figure 16.14C Thermoacidophile habitat and structure
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Boiling springs and geysers in Sulfolobus
Yellowstone National Park acidocaldarius
(geysers): © JeffLepore/Photo Researchers, Inc.; (inset): Courtesy Dennis W. Grogan, University of Cincinnati
16-47

48. 16.15 Prokaryotes have medical and
environmental importance
 Vast majority of bacterial species are not
pathogenic to humans
 Some bacteria are pathogenic
 Tuberculosis (TB) kills more people worldwide than any other
infectious disease
 Caused by Mycobacterium tuberculosis
16-48

49. 16-49

50. Prokaryotes are important in the environment
 Ancient photosynthetic cyanobacteria released
copious amounts of oxygen
 Bacteria break down and recycle nutrients in the soil
 Prokaryotes play an essential role in the carbon
nitrogen, sulfur, and phosphorus environmental cycles
16-50

51. HOW BIOLOGY IMPACTS OUR LIVES
16D Disease-causing Microbes Can Be
Biological Weapons
 Biological warfare is the use of viruses and
bacteria, or their toxins, as weapons of war
 Bioterrorists prefer pathogens that are
 Highly contagious, consistently produce a desired
detrimental effect on a population, have a short
incubation period, and are easy to disseminate and
deliver to a population
 In addition to humans, valuable animals and
crops can be the targets of biological attacks
 Vaccines and preventives may be the best way
to counter biological agents 16-51

52. Connecting the Concepts:
Chapter 16
 Viruses are noncellular, disease-causing agents
 Prokaryotes are cellular, but their structure is
simpler than that of eukaryotes
 Many prokaryotes can live in extreme
environments.
 Not all bacteria cause diseases, but the few that
do infect humans can be deadly. 16-52