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Chapter 27:
Prokaryotes
Cutting Board (Eubacteria)
What are Prokaryotes?
Morphological Diversity
See text for a better
look at these, but no
need to memorize
these or associated
information
Common Bacterial Shapes
Spirochete
Cyanobacteria (blue-green algae)
Cyanobacteria are
oxygen-liberating
photosynthetic
bacteria
A Prokaryotic Cell
Bacterial Cell Walls
Peptidoglycan is material making up bacterial cell wall
Thicker peptydoglycan layer
but no outer membrane
Thinner peptydoglycan
layer and outer
membrane
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)
Gram Stain
Pink are Gram
negative
Purple are Gram
positive
Bacterial Capsule
Capsules
provide
desiccation
resistance,
attachment to
surfaces, and
resistance to
phagocytosis
Bacterial Fimbriae
Fibriae are
involve in
bacterial
attachment to
surfaces and
resistance to
phagocytosis
Conjugation
Sex pili effect the
transfer of conjugative
plasmids
Bacterial Flagella
Flagella
effect
motility
Movement can
be down or up
concentration
gradients,
e.g., toward
food
Flagella
Invaginated Plasma membranes
Some prokaryotes display
invaginated plasma
membranes
This increases
membrane area, just as
seen, e.g., in
mitochondria
Endospores
Some bacteria
can form
endospores,
which are nonreplicative cell
forms that are
highly resistant
to
environmental
insult
Endospores
Biofilms
Surface
coating
colonies of
bacteria (often
of more than
one type) are
called biofilms
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
Oxygen Requirements
Bacterial Nutrional Modes
Know that outside parentheses
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 nonatmospheric 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)
Specialized N2-Fixing Cells
Nitrogen-fixing
cyanobacteria
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
Comparisons…
Comparisons…
 Symbioses are intimate, relatively long-term
interaction between organisms
Symbiosies
 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
Example: Mutualism
It is mutualistic bacteria that
produce the glow in these fish
 Bacterial parasites typically have some means
by which they can harm the host organism,
such as by producing toxins
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
Bacterial Diseases
The End