Production of Docosahexaenoic Acid by Marine Aurantiochytrium sp. in Fed-batch Fermentation

Docosahexaenoic acid (a polyunsaturated fatty acid) plays an important role in the prevention of arteriosclerosis and cardiovascular diseases. Thraustochytrid protists, specifically Aurantiochytrium strains, are among the main microbial producers of omega-3 fatty acid. The aim of the present study was to enhance biomass, oil, and docosahexaenoic acid (DHA) content of Aurantiochytrium sp. by glucose or glycerol feeding in a 3L-fermentation system.

A native strain of Aurantiochytrium sp. qe-4 (KR091914.1) was used for DHA production. Glycerol and glucose were used as a carbon source in a defined medium. Cell growth, lipid, and DHA accumulation in Aurantiochytrium sp. were studied under fed-batch cultivation by using accurate feeding techniques in a 3 L fermentor.

The results of the present study indicated that at C/N ratio of 1.5 and medium composition of 30 g.L-1 glycerol, 10 g.L-1 peptone, and 10 g.L-1 yeast extract, the native strain of Aurantiochytrium produced 30.2 g.L-1 biomass, 8.8 g.L-1 lipid, and 1.7 g.L-1 DHA. Also at C/N ratio of 2 and medium composition of 40 g.L-1 glucose, 20 g.L-1 mono-sodium glutamate (MSG) and 6 g.L-1 yeast extract, 27.6 g.L-1 biomass, 12.5 g.L-1 lipid, and 1.45 g.L-1 DHA were produced. It was also shown that low dissolved oxygen less than 3% of saturation was efficient for DHA production.

During the fermentation process, dissolved oxygen values and carbon-to-nitrogen ratios are critical factors that influence growth and DHA synthesis in Aurantiochytrium. These results showed that the native strain of Aurantiochytrium had a better performance to produce DHA in a medium containing glycerol than glucose as the sole carbon source.