High density cultivation of biomass in fed-batch system with DO-stat.

Abstract

Escherichia coli and Candida brassicae were cultivated in a fed-batch culture with a DO-stat under the condition that none of the components in the basal medium limited the growth of the microorganism. High densities of biomasses (125 g/l for E. coli and 138 g/l for C. brassicae) were obtained. The final biomasses obtained in the cultivations of E. coli and C. brassicae corresponded to 57% and 51%, respectively, of the limits that the organisms can be cultivated in view of viscosity of the broth. Metabolic products in the supernatant of the broth at the end of the cultivation and concentration of carbon dioxide in exit gas from the fermentor were measured, and the relations between cell concentration and growth yield with respect to carbon source were shown. It was considered that the decreases in growth yield and specific growth rate in the case of E. coli were due to the metabolites, including CO2, which increased to inhibitory concentrations. On the other hand, the possibility of obtaining a higher density of biomass was shown in the case of C. brassicae if a fermentor with higher oxygen transfer rate were used. Merits of using pure oxygen gas for production of biomass were exemplified.