Fed-batch cultivation of the docosahexaenoic-acid-producing marine alga Crypthecodinium cohnii on ethanol

Abstract.

The heterotrophic marine microalga Crypthecodinium cohnii produces docosahexaenoic acid (DHA), a polyunsaturated fatty acid with food and pharmaceutical applications. So far, DHA production has been studied with glucose and acetic acid as carbon sources. This study investigates the potential of ethanol as an alternative carbon source for DHA production by C. cohnii. In shake-flask cultures, the alga was able to grow on ethanol. The specific growth rate was optimal with 5 g l^–1 ethanol and growth did not occur at 0 g l^–1 and above 15 g l^–1. By contrast, in fed-batch cultivations with a controlled feed of pure ethanol, cumulative ethanol addition could be much higher than 15 g l^–1, thus enabling a high final cell density and DHA production. In a representative fed-batch cultivation of C. cohnii with pure ethanol as feed, 83 g dry biomass l^–1, 35 g total lipid l^–1 and 11.7 g DHA l^–1 were produced in 220 h. The overall volumetric productivity of DHA was 53 mg l^–1 h^–1, which is the highest value reported so far for this alga.