Effect of culture conditions on the growth rate and lipid production of microalgae Nannochloropsis gaditana

Microalgae Nannochloropsis gaditana (CCMP527) is an ideal candidate as a renewable and sustainable alternative oil source to traditional fossil fuel. It has advantages including high oil content, short growth cycle, and high biomass yield. Experimental data showed that with 5% CO₂ enriched air and tris-HCl buffered f/2-Si medium, a maximum growth rate of 0.48 day^-1 and a lipid yield of 0.32 g/l were achieved. Various carbon and nitrogen sources were investigated to determine the range of substrates that may be feasible for cultivation with minimal impact on productivity. The sources evaluated cover some of the compounds found in fertilizers and groundwater. When glucose was added into the medium, microalgae grew faster mixotrophically but the lipid yield was reduced by 86%. Adding high concentrations of nitrogen, 10 mM N in the form of nitrate, ammonium sulfate, glycine, and urea, resulted in variations in lipid yield from 0.02 g/l to 0.27 g/l. However, the growth rate increased slightly to 0.52 day^-1 at the higher nitrogen concentration when nitrate and urea were the nitrogen sources. The major fatty acids were C16:0 and C16:1 regardless of the carbon and nitrogen sources, which are readily converted to fuels. While the amount of nitrogen affects productivity, the types of fatty acids produced are not affected hence making cultivation on impaired waters feasible.