Nitrate repletion strategy for enhancing lipid production from marine microalga Tetraselmis sp.

•A two-stage process was applied to enhance the lipid productivity of Tetraselmis sp.•Nitrate repletion enhanced both the cell growth and lipid content of Tetraselmis sp.•Nitrate depletion resulted in the lowest lipid productivity from Tetraselmis sp.•The fraction of polyunsaturated fatty acids (PUFAs) increased under N repletion.

The cell growth rate and cellular lipid content of microalgae are affected by the nitrogen levels during cultivation. The growth rate and lipid content of marine microalga Tetraselmis sp. was found to increase under nitrate replete conditions, but not under deplete conditions. Thus, in order to enhance the lipid productivity of Tetraselmis sp., a two-stage culture process utilizing nitrate replete condition was applied. When the cells were cultivated in F/2 medium for five days in the first stage, the obtained lipid content and productivity were 22.4% and 26.7 mg L−1 d−1, respectively. After second stage of cultivation for a further 36 h under nitrate replete conditions with 8.82 mM NaNO3, increased biomass concentration of 1.32 g L−1 and lipid content of 30.5% were obtained, with an enhanced lipid productivity of 47.3 mg L−1 d−1.