A mathematical model is presented which qualitatively describes the growth kinetics of the aphid-pathogenic Erynia neoaphidis in liquid culture. An essential feature of the model is that it allows for the presence of a toxic component within the growth medium which may be broken down by an extracellular enzyme released by the biomass. In this investigation, the toxin was oleic acid which had previously been shown to be essential for the growth of E. neoaphidis, but only at low concentration.

The model reproduces a number of unusual features of the kinetics of growth of E. neoaphidis in liquid culture. These include: the requirement for a high inoculum concentration to successfully initiate growth in liquid culture; failure to grow in continuous culture under conditions similar to those supporting successful batch culture; a reduced growth yield in continuous culture compared to batch culture; a depressed apparent specific growth rate in continuous culture compared to batch culture and, deviation from the usual exponential decrease of biomass concentration during washout. Through the development of the model, and the application of predictions derived from it to the laboratory situation, continuous culture of E. neoaphidis was achieved for the first time.