Chemostat vs. Turbidostat — What's the Difference?

Chemostat and turbidostat are bioreactor devices used for growing microorganisms under controlled conditions. A chemostat operates by maintaining a constant growth rate of microorganisms by diluting the culture with fresh medium at a fixed rate, thereby controlling the availability of nutrients. On the other hand, a turbidostat maintains a constant cell density or turbidity by adjusting the dilution rate in response to changes in cell concentration, ensuring that the culture does not become too dense or dilute.

Chemostat and turbidostat serve distinct purposes in microbial research. In a chemostat, the concentration of a limiting nutrient is kept constant to study the microbial growth rate and yield. Turbidostat, conversely, is designed to maintain a constant optical density or turbidity of the culture, which allows for the study of microbial physiology and metabolism at different growth phases, especially at high growth rates.

The underlying mechanisms of chemostat and turbidostat are inherently different. In a chemostat, the dilution rate is constant, and the growth rate is determined by the concentration of the limiting nutrient. In contrast, a turbidostat has a variable dilution rate which is automatically adjusted based on the turbidity or cell density of the culture, allowing for continuous growth of microorganisms without nutrient limitation.

When employing a chemostat or a turbidostat, the choice depends on the research objectives. Researchers select a chemostat when they need to investigate the effects of nutrient limitation on microorganisms. In contrast, a turbidostat is the device of choice when studying cellular responses under constant environmental conditions without the constraint of nutrient limitation, especially during the exponential growth phase of microorganisms.