Production of docosahexasaenoic acid (DHA) by a native Labyrinthulomycetes strain, Thraustochytriidae sp. TN5, whose growth characteristics present some differences to related strains, was scaled from shaken flask to a laboratory fermentor. The effect of the growth medium composition and growth conditions for (i) biomass production, (ii) lipid content of the biomass, and (iii) DHA content in the lipids was determined. Taguchi's design of experiments was used to study the influence of two discrete – carbon and nitrogen sources – and six continuous – concentrations of the carbon and nitrogen sources, yeast extract and artificial seawater, incubation temperature, and time- factors on the three mentioned variables. In the flask experiments the lipidic content in the biomass (25.2% w/w) and DHA concentration (0.48 g/L) were the highest at the following conditions: maltose 20 g/L, sodium glutamate 2.4 g/L, yeast extract 6 g/L, 72 h, 25°C, and artificial seawater 30% v/v; under these conditions biomass concentration was 5.1 g/L. Fed-batch allowed to increase biomass concentration to 14 g/L. The lipidic fraction of Thraustochytriidae sp. TN5 biomass in the repeated batches was found between 16.2 and 34.8% w/w. Under this growth condition lipids and DHA productivities were 50 and 23 mg/(L h), respectively.
Practical applications: Consumption of long chain-polyunsaturated fatty acids (LC-PUFA) belonging to the omega-3 family such as DHA has several positive effects on human and animal health. However, natural sources are restricted to cold-water fish and their oils. Marine protists are also good candidates for the production of microbial DHA. For evaluating the potential of new strains the effect of the growth medium composition, growth conditions, and cultivation mode on DHA productivity has to be determined. In this work the production of DHA by a native Labyrinthulomycetes strain was scaled from shaken flask to a laboratory fermentor with the aid of Taguchi's methodology, process in which biomass concentration, lipid content in the biomass, and DHA content in the lipids were increased.