Extremophiles Flashcards
(21 cards)
Extremophiles
grow best under extreme conditions and may not survive
under “normal” conditions (“philes” means “loving”)
Extremotolerant
can tolerate extremes but grow best under “normal”
conditions
Mesophiles
prefer “normal“ conditions and often won’t grow at all under
extreme conditions
water availability
Environmental conditions can cause water to move into or out of a cell
Osmosis: movement of water across a selectively permeable
membrane from dilute solutions to more concentrated solutions
For cells, the selectively permeable membrane is the plasma membrane. Water can move
across it but many solutes can’t.
Tonicity
If the concentration of solutes in the solution is the same as the concentration
inside the cell, the solution is called isotonic (“iso” means “the same”). No
water movement
If the concentration of solutes in the solution is higher than inside the cell, the
solution is called hypertonic (“over”, or “above”). The solution has less
available water than the cell, so water moves out of the cell
If the concentration of solutes in the solution is lower than inside the cell, the
solution is called hypotonic (“less than”). The solution has more available
water than the cell, so water moves into the cell
Xerophiles/Osmophiles
Microbes which can grow over a range of water activities
Halophiles
Halophiles are a special class of osmophile which
specifically live in high salt environments
Not only do they have to cope with low water activity,
they must also withstand high salt concentrations
Acidophiles
grow best between pH 0 and 5.5
Neutrophiles
grow best between pH 5.5 and 8.0
Alkalophiles
grow best between pH 8.0-8.5 and 11.5
Poikilothermic
they can’t regulate their
temperature so it varies with the environment around them
Cardinal growth temperatures
minimum, maximum, and
optimum temperatures for
growth
Psychrophiles
Low-temperature loving microbes
They grow optimally <15°C, and usually will not
grow above 20°C
Mesothermic
microbes grow at relatively normal
temperatures where most living things could
survive
Growth optimum of 20 to 45°C
This includes all human pathogens (remember,
humans regulate their core temperature at
around 37°C)
(Hyper)thermophiles
optimal temperatures above 50
°C
They have the opposite problems to psychrophiles: high
temperatures increase the fluidity of membranes to the point
that they cannot control what moves across them
Proteins may also denature, as the bonds which normally
hold the amino acid chain in the appropriate structure break
with the increased heat
More disulphide bonds between cysteine residues in a
protein help to hold it in the correct shape
These form covalent bridges between different chains of the protein
(Hyper)thermophiles may also make “chaperones”, proteins
which help to hold together and stabilise other proteins
Heat denatures DNA
obligate aerobes
MUST have O2 for growth
Facultative anaerobes
do not require O2 for growth, but do grow
better with it
Aerotolerant anaerobes
ignore O2 and grow equally well whether it
is present or not
Obligate anaerobes
strict anaerobes which do not tolerate O2 and
die in its presence
Microaerophiles
are damaged by the normal atmospheric level of
O2 (20%) but require lower levels (2 to 10%) for growth
Barotolerant and Barophilic
Barotolerant microbes can tolerate higher pressures, whereas
barophilic species will grow at ~700 atm, but not below 500 atm of
pressure
