Kinetic analysis of batch and continuous culture of Streptococcus cremoris HP

Abstract

The growth of Streptococcus cremoris on a semidefined medium was studied at initial lactose concentrations of 0.2–5.0% in batch culture, and in lactose-limited chemostat cultures at 0.5% lactose. Kinetic analysis of the batch data, using statistical techniques, indicated the importance of lactose limitation and lactic acid inhibition of the growth of S. cremoris. A model for the biomass production, lactose utilization, and lactic acid production in batch culture was proposed. In continuous culture, it was found that steady state populations were maintained at higher dilution rates (D = 0.6–0.7 h−1) than the maximum predicted by batch culture (0.56 h−1). No evidence for a selection of fast-growing mutants was obtained. Copious growth adhering to the walls of the fermentor (i.e. wall growth) occurred very rapidly at higher dilution rates and this undoubtedly affected steady-state growth and wash-out and, as a consequence, the apparent maximum dilution rate.