Modulating lipid accumulation and composition in microalgae by biphasic nitrogen supplementation

A biphasic nutritional strategy was employed for enhancing lipid accumulation in the three selected microalgae Chlorella sp. MIC-G4, Chlorella sp. MIC-G6 and Scenedesmus sp. MIC-G8, involving supplementation with different nitrogen sources (NaNO3, KNO3, urea and (NH4)2CO3), followed by their limitation. NaNO3 was found to be the best for enhancing lipid accumulation. Palmitic, linoleic and alpha linolenic acids were the most abundant fatty acids. MIC-G6 recorded the highest content of α- linolenic acid (43.7% of total fatty acid) after 32 d growth in nitrogen rich medium and 36.0%, after 24 d growth in nitrogen rich medium followed by 8 d in nitrogen limited medium. An enhancement of 40–50% in lipids on dry weight basis was recorded in Chlorella sp. MIC-G4 and Scenedesmus sp. MIC-G8, in the treatment involving 24 d growth in nitrogen rich medium, and 8 d in nitrogen limited medium. An abundance of 92–97% (% of total fatty acids) of C16–C18 fatty acids was recorded. Our study illustrates the promise of MIC-G4 and MIC-G8 as a source of lipids, triggered by the biphasic mode of cultivation, and the need to undertake in-depth gene expression profiling to enhance further the lipid accumulation.

► Screening of microalgal isolates for lipid content undertaken
► Chlorella sp. MIC-G4, Chlorella sp. MIC-G6 and Scenedesmus sp. MIC-G8 were most promising.
► NaNO3 supplementation followed by its limitation enhanced lipids by 40–50%
► Palmitic, linoleic and alpha linolenic acids were most abundant.
► Chlorella sp. MIC-G6 recorded the highest content of α-linolenic acid.