The theory of fed batch culture with reference to the penicillin fermentation

A batch culture of microbes fed continuously with culture medium is described as a “fed batch culture”. When a portion of a “fed batch culture” is withdrawn at intervals the system is described as a “repeated fed batch culture”. A fed batch culture may reach a “quasi-steady state” in which the specific growth rate (μh−1) virtually = the dilution rate, that is, the ratio of medium flow rate to culture volume. In a quasi-steady state the specific growth rate gradually decreases. A unique feature of a fed batch culture is that it allows continuous reproduction of the transient conditions between two specific growth rates, which can be chosen at will. Fed batch culture may be used to determine the relation between specific growth rate and the growth-limiting substrate concentration and to determine the maintenance energy. Simple relations are derived to enable the concentrations of products to be predicted. The effects of different cycle times in repeated fed batch culture applied to the pencillin fermentation are discussed. Repeated fed batch culture should find a major application in the production of secondary metabolites which often are synthesised at maximum rates only transiently.