Continuous Cultures (Chemostats)

Continuous culture is an “open”-culture system for the cultivation of microorganisms or cells in which fresh sterilized medium is introduced at a steady flow rate and from which the culture fluid emerges at the same rate. Many types of continuous culture methods exist of which the most common is the chemostat. Chemostats allow for steady-state concentrations of growth-limiting substrates to be maintained at a fixed level in the culture fluid, which results in highly reproducible “steady-state” growth conditions in which changes in cell density, physiological state, and medium composition of the culture are no longer detectable. Growth under nutrient limitation results in submaximal growth rates, which can usually emulate the state of most natural environments far better than what can be achieved with batch cultures. In continuous cultures, nearly all environmental parameters including pH, oxygen tension, population density, and concentration of excretion products can easily be controlled.