Bacteria Slow Growth Advantage
Date: January 2007
I am confused about a statement I heard that there were
advantages to growing bacteria slowly such as at room temperature. What
advantages would this procedure provide in research?
The growth of a bacterial culture has 4 typical phases: Phase 1. is an
induction period in which little growth of the colony occurs. Presumably
the microbes are getting used to their new home! Phase 2. is the
exponential period where (provided there is a surplus of nutrient, no
competing bacteria, and the organisms are not interfering with one another
the number (N) of bacteria (or colonies) follows the equation: N = No
exp(Kt) where No is the initial population, 'exp' is the exponential
function, 't' is the time, and 'K' is a growth constant that depends upon
many factors. At some period of time bacteria begin to slow their growth
for any number of reasons -- they begin to die, the are running out of
food, there is some sort of predator that is feeding on them, and so on.
That is Phase 3. and the net population becomes a constant. After a while,
food, oxygen, space, etc. runs out and the microbes begin to die faster
than they are replaced by their replication. Then N decreases.
There could be a number of advantages to slowing the growth, for example
by keeping the culture at lower temperature (although there could be other
ways of doing this). The investigator may wish to study some aspect of the
growth process, for example some bacterial byproducts, size, shape,
migration, and so forth. If Phase 1. and/or Phase 2. occur too rapidly, the
time "window" available to the investigator may to inconveniently small and
a slower growth pattern may be more desirable. See:
which has some more details.
One reason that you might want to grow bacteria at a lower temperature is if
you're trying to express a toxic protein in E. Coli so that the protein can
be purified and studied. By growing the bacteria at a lower temperature
(usually bacteria are grown at 37C) the protein is expressed at a lower
rate, which gives the bacteria more time to adjust to the foreign protein.
Stanford Department of Chemistry
Some bacteria may not be adapted to growing at elevated temperatures
because they never encountered this condition in their natural environment.
For example, bacteria that are adapted to growing around the polar icecaps
would probably not be capable of growing at temperatures above room
temperature because this "high" temperature might denature one or more of
their essential enzymes.
Ron Baker, Ph.D.
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Update: June 2012