Chapter 27
Prokaryotes
“All the world’s bacteria essentially have access to a single gene pool and hence to
the adaptive mechanisms of the entire bacterial kingdom. The speed of recombination
over that of mutation is superior: it could take eukaryotic organisms a million years to
adjust to a change on a worldwide scale that bacteria can accommodate in a few
years.” --Lynn Margulis
Characteristics of Prokaryotes
Very small--1-5 m
in diameter.
Comes in a wide
variety of shapes:
 Bacilli
 Cocci
 Spirilla
Characteristics of Prokaryotes
Has a cell wall, provides many functions:
 Helps it maintain its shape
 Provides protection
 Keeps the cell from bursting in hypotonic environments.
Prokaryotic Cell Wall
 The cell wall of a prokaryotic cell is different from that of a
eukaryote:
 Eukaryotic cell walls are made of cellulose or chitin.
 Prokaryotic cell walls contain peptidoglycan--modified sugar
polymers cross-linked to short peptides.
 Archean cell walls contain a variety of polysaccharides but lack
peptidoglycan.
Gram Staining
Hans Christian Gram developed the Gram
staining technique and it is used to classify
many bacterial species into 2 categories.
 Gram positive
 Gram negative
Gram Positive Bacteria
Gram positive bacteria have a large amount
of peptidoglycan in their cell walls.
60-90% of the entire wall.
They have very little protein (except
streptococci).
Gram Positive Bacteria
Their thick cell walls allow them to retain the
crystal-violet dye.
Yeast cells have thick walls and no peptidoglycan
but still retain the stain. Wall thickness, not
peptidoglycan.
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Gram Negative Bacteria
Gram negative bacteria have less
peptidoglycan (thin cell wall), and cell walls
that are structurally more complex.
10-20% of wall is peptidoglycan.
They have an outer bilayer membrane that acts as
a coarse sieve.
Gram Negative Bacteria
Gram negative bacteria have less
peptidoglycan (thin cell wall), and cell walls
that are structurally more complex.
It has little control over the movement of
substances into and out of the cell.
It does control the movement of proteins.
Gram negatives are less sensitive to penicillin
because this sieve acts to keep penicillin out.
Gram Negative Bacteria
Their outer membrane contains the
endotoxin lipopolysaccharide.
No retention of the crystal violet-iodine stain
due to the thin cell wall and large amount of
lipoprotein and lipopolysaccharide.
Gram Negative Bacteria
Many pathogenic prokaryotes are Gram
Negative: they usually cause illness by
producing endotoxins.
Gram Negative Bacteria
Endotoxins are lipopolysaccharides released
by the outer membrane of Gram negative
bacteria when they die and their cell walls
break down.
The bacteria that produce endotoxins are not
normally found in healthy animals.
Examples: cholera, botulism, salmonella
Usefulness of Gram Staining
 Gram staining is useful in medicine.
 Gram negative bacteria are usually more
pathogenic and the LPS is usually toxic and
sometimes lethal.
 Gram negatives are often more resistant to
antibiotics due to the outer membrane.
 The outer membrane of Gram negatives protect
against the body’s defenses.
 Some prokaryotes contain a capsule which is a sticky outer
coat of polysaccharide or protein which shields the bacteria
from the host’s defense system.
Structural Differences Between
Prokaryotes and Eukaryotes
The flagella of prokaryotes are much
different from those of eukaryotes.
Prokaryotic flagella are much smaller.
Structural Differences Between
Prokaryotes and Eukaryotes
The flagella of prokaryotes are much
different from those of eukaryotes.
Prokaryotic flagella are much smaller.
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Structural Differences Between
Prokaryotes and Eukaryotes
Although prokaryotes lack internal organization and
membranous organelles, they can have internal
membranes that perform certain functions--infoldings
of the plasma membrane.
Some membranes similar to cristae--function in cell
respiration.
Others have thylakoid membranes.
Structural Differences Between
Prokaryotes and Eukaryotes
Eukaryotic chromosomes have about 1000x
as much DNA as do prokaryotes.
Prokaryotes’ chromosomes are circular vs.
linear; there is hardly any protein associated
with them.
Prokaryotic DNA is found in the nucleoid
region, eukaryotic in the nucleus.
Prokaryotic DNA is often associated with
plasmids.
Plasmids
Recall, plasmids are small rings of DNA with a
few genes that usually confer some sort of
benefit to the bacterium.
Plasmids often increase a bacterium’s chance
of survival in certain environments, but they
are not essential to survival.
Plasmids
Plasmids generally
have contingency
functions:
Provide resistance to
antibiotics
Direct the metabolism
of rarely encountered
nutrients.
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The Success of Prokaryotes
Prokaryotes are successful because they can
reproduce quickly--via binary fission.
Typically a 1-3 hour generation time.
Some every 20 minutes in optimal conditions.
36 hours would cover the Earth in 18” of bacteria
3 days would exceed the mass of the Earth
They are limited by metabolic wastes, food
supply and consumption by other organisms.
The Success of Prokaryotes
The success of prokaryotes is also due to
their ability to withstand harsh environments.
Natural selection has enabled prokaryotes to
adapt quickly to changing environments.
Their fast generation time allows them to
propagate mutations quickly.
These mutations are often beneficial to survival.
Some bacteria form endospores when the
environment becomes harsh.
Endospores
Endospores are produced when the
prokaryote wraps a copy of its DNA in a
tough wall and then removes the water.
The metabolism inside the spore comes to a
halt a picks up again when conditions
improve.
Metabolism in General
Phototrophs-obtain energy from light.
Chemotrophs-obtain energy from chemicals
in the environment.
Autotrophs-only need CO2 as a carbon
source, they make everything else they need
themselves.
Heterotrophs-require at least one source of
organic carbon to sustain themselves.
Prokaryotic Metabolism
There are a number of different ways for
organisms to obtain energy and carbon.
On the whole, prokaryotes are much more
diverse than eukaryotes.
All nutrition types seen in eukaryotes are
found in prokaryotes. Prokaryotes also have
other means of obtaining energy and carbon.
Prokaryotic Metabolism
With respect to oxygen, a prokaryote’s
metabolism can vary.
Obligate aerobes require oxygen to survive.
Facultative anaerobes use O2, but can get
along without it.
Obligate anaerobes are poisoned by O2.
Some obligate anaerobes live exclusively with
fermentation. Others obtain energy from
anaerobic respiration. Substances such as NO3and SO42- accept electrons in the place of O2 at
the end of the ETC.
Prokaryotic Metabolism
Nitrogen metabolism. Nitrogen is essential
for the production of amino acids.
Eukaryotes are limited by the types of nitrogen
compounds they can use.
Prokaryotes can use nitrogen from a wide variety
of sources.
Nitrogen fixation is the process by which
certain prokaryotes use N2 to make NH3. The
NH3 is then used along with CO2 and H2O to
create a wide variety of organic molecules.
Prokaryotic Metabolism
There are four main modes of nutrition:
1. Photoautotrophs
2. Chemoautotrophs
3. Photoheterotrophs
4. Chemoheterotrophs
1. Photoautotrophs
Are photosynthetic organisms that use light
energy to drive the synthesis of organic
compounds from CO2.
Examples: cyanobacteria, plants, algae
2. Chemoautotrophs
These oxidize inorganic substances (H2S,
NH3, and Fe2+) and use CO2 as a carbon
source to drive the synthesis of organic
compounds.
*This is unique to prokaryotes.
3. Photoheterotrophs
Use light energy and carbon from an organic
source for nutrition.
*Many marine prokaryotes use this.
4. Chemoheterotrophs
Consume organic compounds for energy and
carbon.
Examples: Found in prokaryotes, protists, fungi,
and animals.
The 2 Domains of Bacteria
1. Bacteria-the vast majority of prokaryotes
of which most people are aware.
Pathogenic-cause infections
Beneficial-produce many foods
2. Archea-share traits with both prokaryotes
and eukaryotes.
Extremeophiles-live in hostile environments where
few other organisms can survive.
Example: extreme thermophiles, extreme
halophiles, methanogens.
Extreme Thremophiles
Live in very hot environments.
Sulfur-rich volcanic hot springs, 90°C+
Genus Sulfolobus.
Deep-sea hydrothermal vents, 113°C
Pycolobus fumarri.
Some grow at temperatures of 600°F+ and
265+ atm of pressure.
Extreme Halophiles
Live in highly saline environments. The Great
Salt Lake, Dead Sea. Some tolerate the salt,
others require it.
Methanogens
Methanogens are named for their mode of
energy production. They use CO2 and oxidize
H2 releasing CH4 in the process.
These bacteria are the strictest anaerobes.
They are poisoned by O2.
The Importance of Prokaryotes
Prokaryotes are important for the cycling of
chemical elements of living and non-living
components of the environment.
Decomposers break down a variety of
substances.
They extract nutrients from a variety of things
such as dead organisms and waste products.
These metabolites are then returned to the
environment.
The Importance of Prokaryotes
Many prokaryotes also convert usable forms
of inorganic compounds into those that can
be used by other organisms.
Examples: autotrophic prokaryotes use CO2 to
make organic compounds which are passed up
the food chain.
Cyanobacteria produce O2 and fix N2 into
compounds other organisms use to make
proteins.
Symbiosis
Symbiosis is the ecological relationship
between 2 organisms of different species.
The host is the larger organism, while the
symbiont is the smaller one.
There are three types of symbiosis:
1. Mutualism
2. Commensalism
3. Parasitism
1. Mutualism
In mutualism, both symbiotic organisms
benefit.
The well being of many organisms depends
on mutualistic prokaryotes.
Example: the human intestines are home to
between 500-1000 species of bacteria that help
us break down food, keep other bacteria at bay,
and activate genes which stimulate our intestines
to produce blood vessels and absorb food.
2. Commensalism
Commensalism is where one organism
benefits where neither of the organisms is
harmed.
These are difficult to document in nature
because any close association between
organisms is likely to benefit both of them.
Hitchihiking species of algae is an example.
3. Parasitism
With parasitism, the symbiont (a parasite)
benefits while the host suffers.
Tapeworms.
Controlling Prokaryotes
Antibiotics have done a good job of
containing disease and preventing death.
However, the rapid production of bacteria
enables them to propagate a mutation that
confers resistance throughout the population.
Natural selection favors these mutants and
allows them to survive.
Usefulness of Prokaryotes
For all of the harm that bacteria cause, we
reap many benefits from them as well.
Can be used to produce vitamins, hormones,
etc.
Bioremediation uses prokaryotes to remove
pollutants from the air, soil, and water.
Biomining
Prokaryotes can also be used to recover
precious metals from ores in a process called
biomining.
 30 billion kg of Cu from copper sulfides each year.
 1 million kg of gold concentrate is processed each day extracting
the gold in Ghana, Africa.
The microbiology of biomining: development and optimization of mineral-oxidizing microbial consortia. Douglas E. Rawlings and D. Barrie Johnson