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Chapter 27
Prokaryotes
Bugs
• They’re (Almost) Everywhere!
• Most are microscopic
– But what they lack in size they more than
make up for in numbers
• The number of prokaryotes in a single handful
of fertile soil
– Is greater than the number of people who have
ever lived
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Metabolically diverse
• thrive almost everywhere
– Includes too acidic, too salty, too cold, or too
hot areas
Figure 27.1
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Prokaryotes
• Structural, functional, and genetic adaptations
contribute to prokaryotic success
• Most prokaryotes are unicellular
– Although some species form colonies
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Prokaryotes
• Most unicellular, some in colonys
– three most common shapes: spheres (cocci),
rods (bacilli), and spirals (spirochetes)
1 m
Figure 27.2a–c (a) Spherical (cocci)
2 m
(b) Rod-shaped (bacilli)
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5 m
(c) Spiral
Cell-Surface Structures
cell wall,
• maintains cell shape,
• provides physical protection,
• prevents the cell from bursting in a
hypotonic environment
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Gram stain
classifies many bacterial species into two groups
based on cell wall composition, Gram-positive and
Gram-negative
Lipopolysaccharide
Cell wall
Peptidoglycan
layer
Cell wall
Outer
membrane
Peptidoglycan
layer
Plasma membrane
Plasma membrane
Protein
Protein
Grampositive
bacteria
Gramnegative
bacteria
20 m
(a) Gram-positive. Gram-positive bacteria have
a cell wall with a large amount of peptidoglycan
that traps the violet dye in the cytoplasm. The
alcohol rinse does not remove the violet dye,
which masks the added red dye.
Figure 27.3a, b
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(b) Gram-negative. Gram-negative bacteria have less
peptidoglycan, and it is located in a layer between the
plasma membrane and an outer membrane. The
violet dye is easily rinsed from the cytoplasm, and the
cell appears pink or red after the red dye is added.
Cell wall
• capsule, sticky layer of polysaccharide or
protein
– To avoid phagocytosis, attach to host cells
200 nm
Capsule
Figure 27.4
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Prokaryotes
• fimbriae and pili
– to stick to substrate or individuals in a colony
Fimbriae
200 nm
Figure 27.5
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Motility
• bacteria propel themselves by flagella
– structurally and functionally different from
eukaryotic flagella
Flagellum
Filament
50 nm
Cell wall
Hook
Basal apparatus
Figure 27.6
Plasma
membrane
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Prokaryotic cells
– Usually lack complex compartmentalization
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Some….
– Do have specialized membranes that perform
metabolic functions
0.2 m
1 m
Respiratory
membrane
Thylakoid
membranes
Figure 27.7a, b
(a) Aerobic prokaryote
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(b) Photosynthetic prokaryote
Genome
– ring of DNA not surrounded by membrane, located
in a nucleoid region
Chromosome
Figure 27.8
1 m
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Bacteria
• Some species
– have smaller rings of DNA called plasmids
• Plasmids can carry toxin or antibiotic
resistance genes
– Prokaryotes reproduce by binary fission
• And can divide every 1–3 hours (20 mins for
E. coli, optimal conditions)
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Endospores
–
Found in many soil bacteria, act like seeds
• Cause botulism in poorly cooked foods
–
can remain viable in harsh conditions for centuries
Endospore
0.3 m
Figure 27.9
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Bacillus anthracis (anthrax)
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Prokaryotic metabolism
• great diversity of nutritional and metabolic
adaptations, can metabolize almost anything
you can think of!
• Four models of nutrition
– Photoautotrophy
– Chemoautotrophy
– Photoheterotrophy
– Chemoheterotrophy
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Nutrition
Table 27.1
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Metabolic Relationships to Oxygen
• Prokaryotic metabolism
– Also varies with respect to oxygen
– Why? Evolution of course!
Cyanobacteria
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Metabolic Relationships to Oxygen
• Obligate aerobes
– Require oxygen
• Facultative anaerobes
– Can survive with or without oxygen
• Obligate anaerobes
– Are poisoned by oxygen
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Nitrogen Metabolism
• Prokaryotes can metabolize nitrogen
• Nitrogen fixation
– Some prokaryotes convert atmospheric
nitrogen to ammonia
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Cooperation in bacteria
• In the cyanobacterium Anabaena
– Photosynthetic cells and nitrogen-fixing cells
exchange metabolic products
Photosynthetic
cells
Heterocyst
20 m
Figure 27.10
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Cooperation
• In some prokaryotic species
1 m
– Metabolic cooperation occurs in surfacecoating colonies called biofilms
Figure 27.11
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The Center for Biofilm Engineering, MSU
A Friendly Guide to Biofilm Basics & the CBE
1. What is biofilm?
You may not be familiar with the term "biofilm," but you have certainly encountered biofilm on a regular basis. The plaque that forms on
your teeth and causes tooth decay is a type of bacterial biofilm. The "gunk" that clogs your drains is also biofilm. If you have ever
walked in a stream or river, you may have slipped on the biofilm-coated rocks.
Biofilm forms when bacteria adhere to surfaces in aqueous environments and begin to excrete a slimy, glue-like substance that can
anchor them to all kinds of material – such as metals, plastics, soil particles, medical implant materials, and tissue. A biofilm can be
formed by a single bacterial species, but more often biofilms consist of many species of bacteria, as well as fungi, algae, protozoa,
debris and corrosion products. Essentially, biofilm may form on any surface exposed to bacteria and some amount of water. Once
anchored to a surface, biofilm microorganisms carry out a variety of detrimental or beneficial reactions (by human standards),
depending on the surrounding environmental conditions.
What is the industrial significance of biofilm?
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Archaea – can live in extreme environments
• Eg. Extreme halophiles
– Live in high saline environments
Figure 27.14
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Prokaryotes
• play a major role in chemical recycling
• Chemoheterotrophic prokaryotes function as
decomposers
• Nitrogen-fixing prokaryotes
– Add usable nitrogen to the environment
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Symbiotic Relationships
– Many live with other organisms in symbiotic
relationships (mutualism and commensalism)
Figure 27.15
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Pathogenic Prokaryotes
• Prokaryotes cause about half of all human
diseases
– Eg. Lyme disease
Figure 27.16
5 µm
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Diseases
• Pathogenic prokaryotes typically cause disease
– By releasing exotoxins or endotoxins
• Many pathogenic bacteria
– Are potential weapons of bioterrorism
– Anthrax, plague, Tularemia (rabbit fever)
– Toxins: botulism
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Caution About a Bioterror Attack on the U.S. Milk Supply
June 2005
STANFORD GRADUATE SCHOOL OF BUSINESS — A mere 4 grams of
botulinum toxin dropped into a milk production facility could cause serious
illness and even death for 400,000 people in the United States. Investments that
would cost the public only 1 cent more per half-gallon of milk could prevent this
nightmare scenario, according to Lawrence M. Wein of the Stanford Graduate
School of Business.
Wein, the Paul E. Holden Professor of Management Science, has been
conducting a series of studies on the effects of various potential terrorist
activities in United States. Not only milk, but soft drinks, fruit and vegetable
juices, processed tomato products, and even grains—anything that goes through
large-scale storage and production and rapid distribution—could be at risk for
such an attack, with catastrophic consequences for the American public, Wein
says in his most recent study, conducted with Yifan Liu, a PhD candidate at the
Institute for Computational and Mathematical Engineering at Stanford
University.
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Bioremediation
– The use of organisms to remove pollutants
from the environment
Figure 27.17
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Also
• major tools in:
– Mining
– The synthesis of vitamins
– Production of antibiotics, hormones, and other
products
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•
Antibiotics produced by Bacteria
•
Antibiotic
Bacterial Species
•
Tetracycline
Streptomyces remosus
•
Streptomycin
Streptomyces griseus
•
Cyclohexamide Streptomyces griseus
•
Neomycin
Streptomyces frodiae
•
Cycloserine
Streptomyces orchidaceus
•
Erythromycin
Streptomyces erythreus
•
Kanamycin
Streptomyces kanamyceticus
•
Lincomycin
Streptomyces lincolnensis
•
Nystatin
Streptomyces noursei
•
Polymyxin B
Bacillus polymyxa
•
Bacitracin
Bacillus licheniformis
•
And streptokinase – clot busting drug from Streptococcus
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