Transcript Nutrition and Growth 2 Microbial Ecology

Microbiology for Health Sciences
Oxygen
Temperature
pH
Osmotic Pressure
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Aerobe: uses oxygen for
metabolism
Facultative Anaerobe: does not
require oxygen for metabolism
Microaerophile: requires small
amounts of oxygen for
metabolism
Strict Anaerobe: require element
other than oxygen for
metabolism, N, S, CO2
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Aerobe: can use gaseous oxygen in its
metabolism and possesses the enzymes
needed to process toxic oxygen products
Obligate aerobe: cannot grow without
oxygen
Facultative anaerobe: an aerobe that does
not require oxygen for its metabolism and
is capable of growth in the absence of it
Microaerophile: does not grow at normal
atmospheric concentrations of oxygen but
requires a small amount of it in
metabolism
Anaerobe: lacks the metabolic enzyme
systems for using oxygen in respiration
Strict, or obligate, anaerobes: also lack the
enzymes for processing toxic oxygen and
cannot tolerate any free oxygen in the
immediate environment and will die if
exposed to it.
Aerotolerant anaerobes: do not utilize
oxygen but can survive and grow to a
limited extent in its presence
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All microbes require some
carbon dioxide in their
metabolism
Capnophiles grow best at a
higher CO2 tension than is
normally present in the
atmosphere
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Temperature:
◦ Psychrophiles: cold-loving
microbes (-10 to 20 degrees
C)
◦ Mesophiles: moderatetemperature-loving microbes
(10 to 50 degrees C)
◦ Thermophiles: heat-loving
microbes (40 to 73 degrees C)
◦ Refrigeration severely retards
the growth of most
pathogenic bacteria
A microorganism that has an
optimum temperature below
15°C and is capable of growth
at 0°C.
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True psychrophiles are
obligate with respect to cold
and cannot grow above 20°C.
Psychrotrophs or facultative
psychrophiles- grow slowly
in cold but have an optimum
temperature above 20°C.
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An organism that grows at
intermediate temperatures
Optimum growth
temperature of most: 20°C
to 40°C
Temperate, subtropical, and
tropical regions
Most human pathogens have
optima between 30°C and
40°C
[INSERT FIGURE 6.4]
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A microbe that grows
optimally at temperatures
greater than 45°C
Vary in heat requirements
General range of growth of
45°C to 80°C
Hyperthermophiles- grow
between 80°C and 120°C
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Temperature Adaptations
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Microbial cells cannot control their
temperature, so they assume the ambient
temperature of their natural habitat
The range of temperatures for the growth of a
given microbial species can be expressed as
three cardinal temperatures:
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Minimum temperature: the lowest temperature
that permits a microbe’s continued growth and
metabolism
Maximum temperature: The highest
temperature at which growth and metabolism
can proceed
Optimum temperature: A small range,
intermediate between the minimum and
maximum, which promotes the fast rate of
growth and metabolism
Some microbes have a narrow cardinal range
while others have a broad one
Another way to express temperature
adaptation- to describe whether an organism
grows optimally in a cold, moderate, or hot
temperature range
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pH: low pH = acidic,
high pH = basic
◦ pH range 0-14
◦ Normal growth range for
bacteria is pH 6 to 8 (most
bacteria can’t grow in
orange juice)
◦ Acidophiles (minority) can
grow in pH 4
◦ Molds and yeasts grow in
pH 4-6
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Majority of organisms
live or grow in habitats
between pH 6 and 8
Obligate acidophiles
◦ Euglena mutabilis- alga
that grows between 0 and
1.0 pH
◦ Thermoplasma- archae
that lives in hot coal piles
at a pH of 1 to 2, and
would lyse if exposed to
pH 7
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Most microbes live either
under hypotonic or isotonic
conditions
Osmophiles- live in habitats
with a high solute
concentration
Halophiles- prefer high
concentrations of salt
Obligate halophiles- grow
optimally in solutions of 25%
NaCl but require at least 9%
NaCl for growth
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Osmotic pressure: addition of
salts to foods results in
shrinkage of cell due to loss of
water
◦ Plasma membrane pulls away
from cell wall which results in
inhibition of cell growth
◦ Ex. In food prep = salted fish,
honey, sweetened and
condensed milk (addition of
high amounts of salt or sugar)
◦ Halophiles: org. that can grow
in high salt concentrations
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Most microbes live in
shared habitats
Interactions can have
beneficial, harmful, or no
particular effects on the
organisms involved
They can be obligatory or
nonobligatory to the
members
They often involve
nutritional interactions
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A general term used to denote a
situation in which two organisms
live together in a close
partnership
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A general term used to denote a
situation in which two organisms
live together in a close
partnership
• Mutualism: when
organisms live in an
obligatory but mutually
beneficial relationship
A general term used to
denote a situation in which two
organisms live together in a
close partnership
• Commensalism: the member
called the commensal
receives benefits, while its
coinhabitant is neither
harmed nor benefited
– Satellitism: when one
member provides
nutritional or protective
factors needed by the
other
A general term used to denote a
situation in which two organisms
live together in a close
partnership
• Parasitism: a relationship in
which the host organism
provides the parasitic microbe
with nutrients and a habitat
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Organisms are free-living and
relationships are not required for
survival
– Synergism: an interrelationship
between two or more free-living
organisms that benefits them
but is not necessary for their
survival
– Antagonism: an association
between free-living species that
arrises when members of a
community compete
• One microbe secretes
chemical substances into the
surrounding environment that
inhibit or destroy another
microbe in the same habitat
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Normal microbiotia:
microbes that normally live
on the skin, in the
alimentary tract, and in
other sites in humans
Can be commensal,
parasitic, and synergistic
relationships