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Name: Andrea
Status: Other
Grade:  Other
Location: N/A
Country: N/A
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.

Vince Calder

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.

Ethan Greenblatt
Ph.D. Candidate
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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