High-cell-density cultivation of Schizochytrium sp. in an ammonium/pH-auxostat fed-batch system

Abstract

Thraustochytrids, in particular Schizochytrium spp., are used for the production of the valuable polyunsaturated fatty acid, docosahexaenoic acid (DHA; 22:6 n-3). Growth of Schizochytrium sp. G13/2S in a defined medium was initially made in shake-flask cultures to determine the optimum concentrations of glucose (100–200 g l⁻¹) and ammonia (∼300 mg l⁻¹) that could be used by this microorganism. In subsequent fermenter cultures, a pH-auxostat method was used to maintain NH₃ from 200–300 mg l⁻¹. During the first 49 h of fermentation, 150 g glucose l⁻¹ produced 63 g cell dry wt l⁻¹. Although growth was not limited by the supply of nitrogen, total fatty acids were at 25% cell dry wt which is more than half the final lipid content of commercially-grown Schizochytrium biomass which uses N-limited medium in the final stages for maximum lipid accumulation. This strategy is therefore useful for the cultivation of Schizochytrium to a high cell density up to the point when lipid accumulation can be triggered by N exhaustion.