EFFECT OF NITRATE ON OIL CONTENT AND FATTY ACID COMPOSITION OF Nannochloropsis SP. AT EARLY STATIONARY GROWTH PHASE

A study was conducted to investigate the effect of different nitrate concentrations (0.03, 0.05, 0.09, 0.18, 0.34 and 0.66 mM) on oil content and fatty acid composition of Nannochloropsis sp. (strain UMT-M3) at early stationary growth phase. Results showed that the biomass production increased approximately 7-folds at 0.34 and 0.66 mM nitrates (p>0.05), which produced between 0.63 to 0.78 g L-1 of cells dry weight. The highest oil content of 13.3% (dry weight basis) was obtained at 0.34 mM nitrate. The analysis of oil revealed that palmitic (C16:0), stearic, (C18:0), oleic (C18:1), linoleic (C18:2), gamma-linolenic (C18:3n6) and alpha-linolenic (C18:3n3) acids were the major type of fatty acids detected in all nitrate treatments. Interestingly, the accumulation pattern for C16:0 was completely in reverse of C18:2 and C18:3n3 in nitrate, ranging from 0.03 to 0.18 mM. The most critical regulatory point occurred at 0.05 mM nitrate, where the highest (p<0.05) accumulation of C16:0 (40.6%) was at the expense of C18:2 (11.4%). Surprisingly, the content of C18:1 (31.0 – 35.0%) was unaffected in all nitrate concentrations. These observations lead to the postulation that the activities of genes, such as 12- and 15-desaturases that regulate the synthesis of C18:2 and C18:3n3 are concerted in actions and are in reverse of palmitoyl-ACP thioesterase gene, which regulated the synthesis of C16:0.