Fundamentals of Microbiology

2.5.4 Continuous culture of microorganisms

A microbial population can be maintained in the exponential growth phase and at a constant biomass concentration for extended periods in a continuous culture system. Two major types of continuous culture systems are commonly used: (1) chemostats and (2) turbidostats.

In a chemostat, a sterile culture medium is fed into the culture vessel. This fresh medium contains a limiting amount of an essential nutrient. Growth rate is determined by the rate of flow of medium through the culture vessel. The medium is fed into the vessel at the same rate as the media containing microorganisms is removed.

The Turbidostat

The turbidostat has a photocell that measures the absorbance or turbidity of the culture in the growth vessel. The flow rate of media through the vessel is automatically regulated to maintain a predetermined turbidity or cell density. The dilution rate in a turbidostat varies and the culture medium lacks a limiting nutrient.