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

Abstract

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 V 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<O.OS) 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 A12- and Al5-desaturases that regulate the synthesis ofC18:2 and C18:3n3 are concerted in actions and are in reverse ofpalmitoyl-ACP thioesterase gene, which regulated the synthesis ofC16:0.