Effect of temperature and nitrogen concentration on lipid productivity and fatty acid composition in three Chlorella strains

The effects of temperature and nitrogen (N) on lipid productivity and fatty acid composition in three Chlorella strains grown at 20 °C, 25 °C and 30 °C in modified Tamiya media with low (7 and 21 mg L− 1 N) and moderate (70 mg L− 1 N) N were investigated. Temperature and N influenced biomass accumulation with the largest biomass accumulation (1697, 1732 and 1809 mg DW L− 1 for the three strains) at higher temperatures and N concentrations. Proteins decreased and lipids increased over time with N-deprivation. Strain, temperature and N concentration influenced lipid productivity with the highest productivity in cultures grown in 3% N at higher temperatures (68, 70 and 90 mg lipid L− 1 day− 1 for the three strains). The fatty acid methyl ester (FAME) profile was similar in the three strains with C16:0 > C18:1n9c > unidentified FAMEs > C18:2n6c > C18:3n3 > C18:0 comprising 90% of the total FAME. C18:1n9c and C16:0 showed the largest variation in response to culture conditions in Chlorella sp. MACC-438 (0.2-26.8% and 2.3-16.2% respectively) and C. minutissima MACC-452 (0.2-26.7% and 3.0-23.3% respectively); unidentified FAMEs (1.1-9.7%) and C18:2n6c (0.9-11.2%) were the most variable in Chlorella sp. MACC-728. Lower temperatures resulted in higher % FAME in Chlorella sp. MACC-438 (68.9%) and C. minutissima MACC-452 (91.7%). Nitrogen concentration had more influence on the specific FAME content compared to temperature. Thus, temperature tolerance is important when selecting strains to ensure high lipid productivity while the specific strains response to N-deprivation is important to ensure quality of the biofuel feedstock.