Chapter 27: Prokaryotes

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Chapter 27Prokaryotes
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Cutting Board (Eubacteria)
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What are Prokaryotes?
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Morphological Diversity
See text for a better look at these, but no need
to memorize these or associated information
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Common Bacterial Shapes
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Spirochete
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Cyanobacteria (blue-green algae)
Cyanobacteria are oxygen-liberating
photosynthetic bacteria
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A Prokaryotic Cell
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Bacterial Cell Walls
Peptidoglycan is material making up bacterial
cell wall
Thinner peptydoglycan layer and outer membrane
Thicker peptydoglycan layer but no outer membrane
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Bacterial Cell Walls
In a hypertonic environment, most prokaryotes
lose water and shrink away form their cell walls
(plasmolyze), like other walled cells. Severe
water loss inhibits the reproduction of
prokaryotes, which explains why salt can be used
to preserve certain foods, such as pork and
fish. pp. 534-5, Campbell Reece (2005)
One of the most important features of nearly
all prokaryotic cells is their cell wall which
maintains cell shape, provides physical
protection, and prevents the cell from bursting
in a hypotonic environment. p. 534, Campbell
Reece (2005)
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Gram Stain
Pink are Gram negative
Purple are Gram positive
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Bacterial Capsule
Capsules provide desiccation resistance,
attachment to surfaces, and resistance to
phagocytosis
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Bacterial Fimbriae
Fibriae are involve in bacterial attachment to
surfaces and resistance to phagocytosis
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Conjugation
Sex pili effect the transfer of conjugative
plasmids
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Bacterial Flagella
Flagella effect motility
Movement can be down or up concentration
gradients, e.g., toward food
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Flagella
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Invaginated Plasma membranes
Some prokaryotes display invaginated plasma
membranes
This increases membrane area, just as seen, e.g.,
in mitochondria
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Endospores
Some bacteria can form endospores, which are
non-replicative cell forms that are highly
resistant to environmental insult
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Endospores
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Biofilms
Surface coating colonies of bacteria (often of
more than one type) are called biofilms
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Bacterial O2 Requirements

• Obligate aerobes require a functioning electron
  transport chain to grow, with O2 as a typical
  final electron acceptor
• Key is their obligate use of an ETS to make ATP
• Also key is their ability grow in the presence of
  oxygen (O2)
• Facultative anaerobes can use O2 as a final
  electron acceptor for their electron transport
  chain (i.e., as aerobes), if available, but can
  grow using only fermentation (no ETS) if O2 is
  not available.
• Obligate anaerobes cannot grow in the presence of
  O2 because they are poisoned by its presence
• Some obligate anaerobes are obligate fermenters
• Other obligate anaerobes are users of electron
  transport chains

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Oxygen Requirements
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Bacterial Nutrional Modes
Know that outside parentheses
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Nitrogen Metabolism

• Together, bacterial species are very adept at
  metabolizing different forms of nitrogen, far
  more adept than are the sum of the eukaryotes
• Nitrogen fixing is the conversion of atmospheric
  N (N2) into bioavailable N (e.g., NH3, ammonia)
• Denitrification is the conversion of
  non-atmospheric N (nitrate and nitrite, NO3- and
  NO2-) to N2 (thus making the nitrogen no longer
  bioavailable except to nitrogen fixers)
• The process by which denitrification occurs is
  known as anaerobic respiration, cellular
  respiration in which something other than O2 is
  reduced as the final electron acceptor
• "In terms of nutrition, nitrogen-fixing
  cyanobacteria are the most self-sufficient of all
  organisms. They require only light, CO2, N2,
  water, and some minerals to grow. p. 539,
  Campbell Reece (2005)

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Specialized N2-Fixing Cells
Nitrogen-fixing cyanobacteria
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Archaea

• Archaea are unusual in terms of the environments
  in which they live, the substrates they consume,
  and the products they release
• Included among Archaea are various extremophiles
• Extreme halophiles, organisms which live in
  extremely salty environments such as inland seas
• Extreme thermophiles, organisms which live in hot
  springs and deep-sea hydrothermal vents
• Mathanogens, which live in anaerobic
  environments, release methane as a metabolic
  waste product, thus producing marsh gas and
  flatulence from cellulose consuming herbivores
  (e.g., cattle, termites)
• Archaea are also found in less extreme
  environments but those species of Archaea have
  not been studied as extensively as Archaea that
  live in extreme environments

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Comparisons
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Comparisons
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Symbiosies

• Symbioses are intimate, relatively long-term
  interaction between organisms
• Typically at least one of the organisms (the
  symbiont) benefits from the relationship
• We can classify symbioses in terms of the degree
  to which the other organism (e.g., the host)
  benefits or is harmed
• Commensalism one organisms benefits while the
  other neither benefits nor is harmed
• Mutualism both organisms benefit
• Parasitism one organism is harmed by the
  symbiont (the parasite)
• A number of bacterial species can enter into
  either Commensal, Mutual, or Parasitic
  relationships with eukaryotic organisms, such as
  animals

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Example Mutualism
It is mutualistic bacteria that produce the glow
in these fish
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Toxins

• Bacterial parasites typically have some means by
  which they can harm the host organism, such as by
  producing toxins
• Toxins are chemical (often protein) agents that
  damage host tissue
• Endotoxin is the Lipid A portion of LPS (not a
  protein) which causes host overreaction
• Endotoxin is produced by Gram-negative bacteria
• Exotoxins are protein toxins, typically produced
  by Gram-positives as exoenzymes or equivalents
• But also many Gram-negatives
• Examples include Neurotoxins and Enterotoxins

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Bacterial Diseases
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The End