Optimum substrate feed rate in fed-batch culture with the DO-stat method

In a fed-batch culture employing the DO-stat method, a rapid increase of dissolved oxygen concentration due to a lack of substrate (the DO signal) is used as an indicator for substrate feeding. The amount of substrate to be fed in response to the appearance of the DO signal is a very important factor for obtaining an optimal fed-batch culture. To select the optimum amount of substrate to be fed at the DO signal, a calculative procedure based on the growth yield, and the relationship between the specific growth rate and substrate concentration is proposed. This procedure is demonstrated in fed-batch cultures of Protaminobacter ruber (a methanol-utilizing bacterium) and Candida brassicae (an ethanol-utilizing yeast). The optimum feed rates calculated with the procedure, 2.5 ml (methanol/l/signal) for P. ruber and 5 ml (ethanol/l/signal) for C. brassicae, both gave good agreement with the cultivation results.