The effect of light, salinity, and nitrogen availability on lipid production by Nannochloropsis sp

Abstract

We examined responses of batch cultures of the marine microalga Nannochloropsis sp. to combined alterations in salinity (13, 27, and 40 g/l NaCl) and light intensity (170 and 700 μmol photons/m(2)·s). Major growth parameters and lipid productivity (based on total fatty acid determination) were determined in nitrogen-replete and nitrogen-depleted cultures of an initial biomass of 0.8 and 1.4 g/l, respectively. On the nitrogen-replete medium, increases in light intensity and salinity increased the cellular content of dry weight and lipids due to enhanced formation of triacylglycerols (TAG). Maximum average productivity of ca. 410 mg TFA/l/d were obtained at 700 μmol photons/m(2)·s and 40 g/l NaCl within 7 days. Under stressful conditions, content of the major LC-PUFA, eicosapentaenoic acid (EPA), was significantly reduced while TAG reached 25% of biomass. In contrast, lower salinity tended to improve major growth parameters, consistent with less variation in EPA contents. Combined higher salinity and light intensity was detrimental to lipid productivity under nitrogen starvation; biomass TFA content, and lipid productivity amounted for only 33% of DW and ca. 200 mg TFA/l/day, respectively. The highest biomass TFA content (ca. 47% DW) and average lipid productivity of ca. 360 mg TFA/l/day were achieved at 13 g/l NaCl and 700 μmol photons/m(2)·s. Our data further support selecting Nannochloropsis as promising microalgae for biodiesel production. Moreover, appropriate cultivation regimes may render Nannochloropsis microalgae to produce simultaneously major valuable components, EPA, and TAG, while sustaining relatively high biomass growth rates.