Chemostat

A chemostat (from Chemical environment is static) is a continuous culture ^[1] device used in microbiology for growing and harvesting microbes.^[2] It consists of two primary parts: a nutrient reservoir and a growth chamber. It can keep a bacterial culture growing at a reduced growth rate over an indefinite time period. Growth of the culture is controlled by the concentration of the limiting nutrient.^[2] The limiting nutrient is a essential growth factor necessary for bacterial growth but present in the media at a concentration such that balanced growth consumes it to r* (a la G. David Tilman) prior to exhausting any other of the essential nutrients in the media. Chemostats allow the the growth rate and yield to be controlled independently. The most important feature of a chemostat is that all fermentation parameters; growth chamber volume, dissolved oxygen, nutrient concentrations, pH, cell density, etc., remain constant throughout the experiment.

Some sources of concern are:

1. Foaming results in overflow with the volume of liquid not exactly constant
2. Some very fragile cells are ruptured during agitation and aeration.
3. Cells may grow on the walls or adhere to other surfaces
4. Mixing may not truly be uniform
5. Dripping the media into the chamber actually results in small pulses of nutrients and thus oscillations in concentrations
6. Bacteria travel upstream quite easily. They will reach the reservoir of sterile medium quickly unless the liquid path is interrupted by an air break in which the medium falls in drops through air.

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Chemostat History

Chemostats were initially developed by Novick and Szilard. They were later refined at Cold Spring Harbor Laboratories and entered the canon of microbiological methods. They diversified rapidly as various control mechanisms led to the auxostat and turbidostat.

Chemostats in Research

Chemostats in research are used for investigations in cell biology, as a source for large volumes of uniform cells or protein. The chemostat is often used to gather steady state data about an organism in order to generate a mathematical model relating to its metabolic processes. Chemostats are also used as microcosms in ecology^[3][4] and evolutionary biology^[5][6][7][8]. In the one case, mutation/selection is a nuisance, in the other case, it is the desired process under study.

Topics in ecology and evolution that have been studied in chemostats include competition for single and multiple resources, the evolution of resource acquisition and utilization pathways, cross-feeding/symbiosis, antagonism, predation, and competition among predators.

Chemostats in Industry

Chemostats are frequently used in the industrial manufacture of ethanol. In this case, several chemostats are used in series, each maintained at decreasing sugar concentrations.

See also

• Biochemical engineering
• Continuous stirred-tank reactor (CSTR)

References