Optical Properties of Nannochloropsis oculata During Progressive Nitrogen Starvation
The marine microalgae Nannochloropsis oculata is known to accumulate lipids, mainly in the form of triglycerides making them an attractive species for renewable biodiesel production. Lipid productivity can be increased by nitrogen starvation of cells causing them to progressively decrease their replication rate in favor of accumulating lipids (up to 70% in dry weight). In addition to nitrogen starvation, recent studies have shown light availability in photobioreactors (PBR) and light received per cell to be important factors in the lipid productivity of the microalgae. These depend on the incident photon flux density, microalgae cell concentration, and the radiation characteristics of the microalgae. The latter complicates the optimization of the lipid production protocols as nitrogen deprivation also causes the cells to progressively decrease their pigmentation thus changing their radiation characteristics. This study presents the overall methodology and the effects of nitrogen starvation on N.oculata. The approach highlighted the strong effect of nitrogen starvation on cell metabolism in addition to the increase in fatty acid content of the cells. These effects were quantified by the progressive changes in the average cell absorption and scattering cross-sections caused by modifications in specific chlorophyll and carotenoid concentrations, cell size distribution.