What is a Chemostat?

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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 10 November 2019
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A chemostat is a device which can be used to cultivate microorganisms at a steady rate. Chemostats allow for continuous cultivation, which means that they can be used to generate a steady supply of microorganisms. There are a number of uses for these devices ranging from research facilities to manufacturing, and several scientific suppliers manufacture chemostats and accessory equipment which people use to operate and control their chemostats, including valves, filters, chambers for growth medium, and so forth.

The way in which a chemostat works is fairly simple. Sterile culture medium which contains a blend of nutrients is dripped into a container, usually through an air break so that organisms inside the device cannot access the sterile culture outside. At the same time, an effluent pipe drains excess medium, keeping the volume levels in the container constant. Microorganisms inside the chemostat will grow on the nutrients, growing at a steady rate as long as the supply of nutrients remains consistent.

By manipulating the flow of nutrients, it is possible to change growth rates. Eventually a maximum growth rate will be reached, beyond which the microorganisms cannot go, but it can take some manipulation to reach this point. The alteration of growth rate can be used to control the speed at which organisms are produced, which can be useful when people are producing microorganisms such as bacteria and yeasts in controlled amounts for specific purposes.


A chemostat can be used to culture a sample, or to grow microorganisms for study and research. The steady supply can allow people to perform a wide variety of experiments, and to quickly trace microorganisms through multiple generations. When there is an industrial use for microorganisms, chemostats are also very useful. For example, yeast can be grown in chemostats and packaged for sale to bakers and brewers who need yeast for their work.

The amount of nutrients supplied per hour divided by the volume of the chemostat is known as the dilution rate. People can change the dilution rate to alter the conditions inside the chemostat. If it is too high, people may lose usable medium through the outflow tube, while if it is too low, organisms may not be able to thrive in the chemostat. Numerous other factors can also influence the growth rate, making it important to use a chemostat in a controlled environment so that issues such as temperature fluctuations can be monitored.


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Post 3

@Charred - Without the ability to control the population, I assume you'd wind up with exponential growth in short order. It would be like the old computer game of "Life" with generations multiplying and multiplying, until the organisms became too many to contain. It also sounds like a B science fiction movie too.

Post 2

@hamje32 - It’s interesting that the bacterial growth has to remain in a level of equilibrium, just like we do, in order to live and thrive.

If they get too much food, the bacteria become unusable. I don’t know exactly what that reference means, but if I get too much food I am unusable for about a day.

Similarly, nutrients that get too little food struggle to survive. So we see that whether you’re talking about life at the micro level or at the macro level, we all have to be in a state of equilibrium to survive and thrive.

Post 1

It’s an interesting device. It reminds me of fermentors which are used to ferment alcohol. They use yeast and bacteria to do the process of fermentation.

I don’t know exactly how the process works but I’d assume that the bacteria or yeast grow too in the process of creating fermentation. In fermentation however you don’t have controlled growth of microorganisms, so the chemostat is very unique.

I can imagine that they can use something like this in industrial science to grow certain organisms with useful properties, such as the ability to “eat” oil slicks or chemical spills.

Scientists could figure out exactly how many organisms they need for the ecological spill and grow only that amount, then release it into the ocean.

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