Prokaryotes and the Origins of Metabolic Diversity

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Chapter 27 Prokaryotes and the Origins of
Metabolic Diversity
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I.  The world of prokaryotes             A. 
Theyre everywhere!                         1. 
Collective prokaryote biomass outweighs all
eukaryotes combined by at least tenfold. 
                          2.  They exist almost
everywhere, including places where eukaryotes
cannot.  
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                        3.  Most prokaryotes are
beneficial we couldnt live without them.  (e.g.
Nitrogen-fixing bacteria)                         
  4.  Some cause illness à bubonic plague,
diphtheria, salmonella                          
5.  Approximately 5000 species have been
identified.  Estimates of prokaryote diversity
range from 400,000 to 4,000,000 species.
            B.  Bacteria and archaea are the
two main branches of prokaryote
evolution                         1.  Archaea are
thought to be more closely related to eukaryotes
than to bacteria.  
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II.  Structure, function, and reproduction of
prokaryotes             A.  Most prokaryotes are
unicellular.                          1.  Some
species form aggregates of two or more
individuals.   B.  Three (3) common shapes 
cocci (round) bacilli (rod) helical (spiral)  
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C.  Prokaryotes are typically 1-5 µm in diameter,
but some can be seen by the naked
eye.                         - Eukaryotic cells
are typically 10-100 µm in diameter.  
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D.  Almost all prokaryotes have cell walls
external to the plasma membrane.                  
       1.  Cell walls maintain cell shape.   2. 
Cell walls are composed of peptidoglycan.
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 3.  There are two types of cell walls.  Bacteria
are grouped according to cell wall type. 
                                    a. 
Gram-positive bacteria have simple, thick cell
walls.  Their cell walls are composed of a
relatively large amount of peptidoglycan.   b. 
Gram-negative bacteria have less peptidoglycan
and are more complex.  They have a peptidoglycan
layer surrounded by the plasma membrane and an
outer membrane.                                   
                 - Gram-negative bacteria are
typically more resistant to host immune defenses
and antibiotics.   Note that the two types of
bacteria can be stained to determine which is
gram-negative (pink) and gram-positive (purple)
using a Gram Stain.
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Gram Positive
Gram Negative
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4.  Most prokaryotes secrete sticky substances
that form a protective layer and enable them to
adhere to substrates.                             
        a.  The sticky protective layer secreted
by prokaryotes is called the capsule.   5.  Some
prokaryotes adhere to substrates using pili. 
                                    a.  Some
pili are specialized for DNA transfer. This
process is called conjugation note for later in
class.  
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 E.  Many prokaryotes are motile        - Some
exceed speeds 100 times their body length per
second.   1.  Modes of movement Note the three
types a.  Flagellum - basal apparatus rotates
the flagellum and propels the cell     b. 
Corkscrew movement of spirochetes (helical) c. 
Some prokaryotes glide over jets of slimy
secretions.  2.  Many prokaryotes move toward or
away from a stimulus taxis.  Chemotaxis is the
movement toward or away from a chemical.
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F.  Cellular and genomic organization of
prokaryotes is different from that of
eukaryotes                         1. 
Prokaryotes have no nucleus.   2.  The nucleoid
region in a prokaryotic cell consists of a
concentrated mass of DNA. This mass of DNA is
usually one thousand times less than what is
found in a eukaryote.   3.  A prokaryote may have
a plasmid in addition to its major chromosome.  A
plasmid is a small ring of DNA that carries
accessory genes. Usually these genes are for
antibiotic resistance!
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Asexual reproduction Fission
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Specialized membranes of prokaryotes
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G.  Prokaryotes grow and adapt rapidly - The
doubling time for E. coli is 20 minutes.  Start
with one E. coli cell.  After 48 hours of
doubling every 20 minutes, the mass of E. coli
would be 10,000 times the mass of the
earth. Bacteria do not have gene transfer by
sexual reproduction, but do transfer genes. Why?
This is an aid in adapting (evolving).   1. 
Three (3) ways for genes to be transferred
between cells a.  Transformation cell takes
up genes from the surrounding environment. b. 
Conjugation direct transfer of genes from one
prokaryote to another. Use the sex pilus to
conjugate. c.  Transduction viruses transfer
genes between prokaryotes.
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Prokaryotic conjugation
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Bacterial transduction
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2.  Endospores are resistant cells formed by some
bacteria as a way to withstand harsh conditions.
The cell replicates its chromosome and wraps it
in a durable wall that can protect the chromosome
from adverse conditions, e.g. boiling water,
desiccation. When the environment is good again,
the cell will revive to a new vegetative
(growing) spore.
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III.  Nutritional and metabolic
diversity             A.  All prokaryotes (and
eukaryotes too) are grouped into four (4)
categories according to how they obtain energy
and carbon .   1.  Photoautotrophs                
                     - Photosynthetic à use
light as the energy source                        
             - CO2 is the carbon
source                                    
Example  Cyanobacteria plants (eukaryotic).
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One of the most independent organisms on earth
Cyanobacteria (Anabaena)
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Cyanobacteria Gloeothece (top left), Nostoc (top
right), Calothrix (bottom left), Fischerella
(bottom right)
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A bloom of cyanobacteria
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Algal blooms
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2.  Chemoautotrophs      - Energy from oxidation
of inorganic substances (e.g. NH4, and S)      -
CO2 is the carbon source          Example 
Sulfolobus, Beggiatoa (shown on
slide)                                            
                    
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3.  Photoheterotrophs      - Light as energy
source      - Organic compounds are source of
carbon   4.  Chemoheterotrophs       - Organic
compounds are energy source and source of carbon
(this includes humans)   Examples  Many
prokaryotes animals (eukaryotic) fungi
(eukaryotic)
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 B.  Metabolic relationships to
oxygen                         1.  Obligate
aerobes       - Use O2 for respiration cannot
grow without it. (Humans are obligate
aerobes)                         2.  Facultative
aerobes       - Use O2 when available ferment
when O2 isnt available.   3.  Obligate
anaerobes       - Poisoned by O2 use
fermentation or live by anaerobic respiration. 
In anaerobic respiration, inorganic molecules
like SO4, NO3, and Fe3 are used instead of
oxygen.
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C.  Photosynthesis evolved early in prokaryotic
life                         1.  Cyanobacteria
started to produce O2 about 2.7 billion years
ago   Contrasting hypotheses for the taxonomic
distribution of photosynthesis among prokaryotes.
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A.  Great diversity of Archaea in extreme
environments and oceans   1.  Two taxa of
archae         a.  Euryarchaeota most
archae         b.  Crenarcheota most
thermophilic species    2.  Examples of
extremophiles         a.  Methanogens produce
methane             - Energy is from hydrogen
gas             - Strictly anaerobic             -
Inhabit swamps and animal intestines  
b.  Extreme halophiles   - Live in
salty environments (Great Salt Lake)              
                                  
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   c.  Extreme thermophiles       - 60- 80 C
optimum temperatures (hot springs)       - 105 C
for deep-sea hydrothermal vents
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Rhizobium N2-Fixing, Lives in Plant Roots of
Legumes
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Chromatium Example of a chemoautotroph Note
the sulfur granules
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Bdellovibrio Bacterial predator
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Myxobacterium Produces cell aggregates and
fruiting bodies
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Heliobacter Causes stomach ulcers
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The remaining four clades and examples for each
are
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 2.  Chlamydias - Parasitic survive only within
cells of animals  - Some cause STDs e.g.
chlamydia
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 3.  Spirochetes       - Helical
heterotrophs      - Some cause STDs e.g. syphilis
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 4.  Gram-Positive Bacteria        - Broad,
diverse group          - Antibiotic producing
bacteria are in this group - Example shown is
Streptomyces (streptomycin) - And (next slide)
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Mycoplasma shown covering a human cell some
species of mycoplasmas cause walking pneumonia
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 5.  Cyanobacteria          - Oxygenic
photosynthesis, and chloroplasts evolved from
them.
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V.  Ecological impacts of prokaryotes 
            A.  Prokaryotes are links in the
recycling of chemical elements   B.  Many
prokaryotes are symbiotic (2 organisms living in
direct contact with each other). There are
three types of symbioses                      1. 
Mutualism both symbiotic organisms
benefit                          - e.g.
Nitrogen-fixing bacteria like Rhizobium plant
obtain organic nitrogen, Rhizobium gets energy in
the form of sugars that the plant produces.
Another example  
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Are all prokaryotes disease producing germs?
Without prokaryotes ecosystems would collapse!
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54.1 An overview of ecosystem dynamics
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Methanogens in Peat
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54.18 The nitrogen cycle
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2.  Commensalism one organism benefits and the
other is not harmed.                              
       - e.g. Bacteria on our skin   3. 
Parasitism parasite benefits and the host is
harmed.               C.  Pathogens cause human
diseases                         - Some
pathogens are opportunistic.  They may be normal
residents of the host, but if the host is
weakened, then they cause disease.  
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Lyme disease Caused by a spirochete
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Red-band disease (RBD) consists of a narrow band
of filamentous cyanobacteria that advances slowly
across the surface of a coral, killing living
tissue as it progresses.
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- How do we know if a particular organism is
responsible for a disease?                        
Robert Koch formed postulates as guidelines to
establish that a disease is caused by a
particular pathogen                              
       a.  Find same pathogen in each diseased
individual.             b.  Isolate the pathogen
and grow it in pure culture.   c.  Inoculate an
individual with the isolated pathogen and the
disease is induced.   d.  Isolate the same
pathogen from the infected individual. This
procedure is called Kochs Postulates and is used
widely to determine what infectious agent causes
disease.
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Most pathogens cause disease by producing
poisons, these are either - Exotoxins proteins
secreted by the pathogen that cause illness.   -
Endotoxins poisons that are part of the pathogen
that causes illness.  (e.g. bacteriums outer
membrane)
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  D.  Humans use prokaryotes in research and
technology                        
Examples Sewage treatment Bioremediation Chemic
al Medical production Research (genetic
engineering, etc.)  
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Figure 27.19 (p. 542) Bioremediation for an oil
spill.
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