Microalgae Isolated from Singapore Mangrove Habitat as Promising Microorganisms for the Sustainable Production of Omega-3 Docosahexaenoic Acid

Docosahexaenoic acid (DHA, C22:6n-3) is an omega-3 fatty acid with beneficial effects for human health. In view of its increasing demand, DHA traditionally produced by marine fisheries will be insufficient, and an alternative sustainable source is urgently required. Here, we report the isolation and characterization of four novel microalgae strains, PLU-A, B, C and D, with a high DHA content of up to 45% from decayed mangrove samples collected from a coastal area in Singapore. Phylogenetic analysis revealed that these isolates were clustered with Schizochytrium sp. TK6 (OK244290.1) and were identified as Schizochytrium sp. strains. A medium optimization with Schizochytrium sp. PLU-D found a glucose-to-yeast extract ratio of 4:1 to be optimal for high biomass and lipid accumulation of up to 70% in shake flasks. In fed-batch fermentation scale-up with the Schizochytrium sp. PLU-D strain, this translates to 175 g/L dry biomass, 94 g/L lipid and 36.2 g/L DHA. Accordingly, the DHA titer obtained is superior to most of the scale-up production reported thus far, while the DHA content is comparable to two other commercially available DHA algae oils. These results suggest that Schizochytrium sp. PLU-D has high potential to be applied for the sustainable production of DHA.