Mixotrophic growth of Phaeodactylum tricornutum on glycerol: growth rate and fatty acid profile

Mixotrophic growth of the eicosapentaenoic acid (EPA) producing diatom Phae odactylum tricornutum UTEX 640 was carried out in 1-L batch cultures under an external irradiance of 165 mu mol photons m(-2) s(-1) by supplementing t he inorganic culture medium with glycerol. The effect on the growth and the fatty acid profile was studied for different initial glycerol concentratio ns (0-0.1 M). The optimal glycerol concentration was 0.1 M. A lag phase was observed at high glycerol concentrations. The present study also shows tha t successive additions of glycerol at 0.1M concentration and using ammonium chloride as a nitrogen source remarkably increased the maximum biomass con centration (16.2 g L-1) and maximum biomass productivity (61.5 mg L-1 h(-1) ). These values were respectively 9 and 8-fold higher than in the photoauto trophically grown control. The level of saponifiable lipids in mixotrophica lly cultured cells was significantly higher than in photoautotrophically cu ltured cells and increased with the glycerol concentration in the medium. T he concentration of storage lipids, saturated and monounsaturated fatty aci ds, were enhanced but the EPA content did not change significantly. The EPA content was around 2.2% of biomass dry weight. The maximum EPA yield was 3 3.5 mg L-1 d(-1) and was obtained in a culture containing 0.1 M glycerol, s upplemented periodically by ammonium chloride. This productivity was 10-fol d higher than the EPA productivity obtained under mixotrophic conditions.