Modelling and parameter identification for batch fermentations with Streptomyces tendae under phosphate limitation.

A simple structured model for the dynamics of phosphate-limited batch fermentations with Streptomyces tendae is presented. The model describes the influence of intracellular phosphate storage upon the growth behav our of the culture. The development of the model takes into account the possible internal regulatory processes of phosphate metabolism. These complex biochemical pathways are summarized with regard to rate-limiting steps to obtain relatively simple model equations. The model parameters are fitted to the experimental data with an identification programme based on the sequential quadratic programming algorithm. Modifications in this algorithm yield a good performance for this application. With respect to the sensitivity of the model parameters, a feedback on the modelling is given. After several loops of modelling and identification, a model was achieved that fits to a set of batch fermentations. Furthermore the simulations show that RNA measurements of some recent fermentations can be interpreted by the simulated internal state variable and that there is evidence for RNA as an intracellular phosphate reserve.