PNNL

Abstract

Abstract: Accurate prediction of algal biofuel yield will require empirical determination of physiological responses to the climate, particularly light and temperature. One strain of interest, Nannochloropsis salina, was subjected to ranges of light intensity (5 – 850 µmol m2 s-1) and temperature (13-40 °C); exponential growth rate, total fatty acids (TFA) and fatty acid composition were measured. The maximum acclimated growth rate was 1.3 day-1 at 23 °C and 250 µmol m2 s-1. Fatty acids were detected by gas chromatography with flame ionization detection (GC-FID) after transesterification to corresponding fatty acid methyl esters (FAME). A sharp increase in TFA containing elevated palmitic acid (C16:0) and palmitoleic acid (C16:1) during exponential growth at high light was observed, indicating likely triacylglycerol accumulation due to photo-oxidative stress. Lower light resulted in increases in the relative abundance of unsaturated fatty acids; in thin cultures, increases were observed in palmitoleic and eicosapentaenoeic acids (C20:5?3). As cultures aged and the effective light intensity per cell converged to very low levels, fatty acid profiles became more similar and there was a notable increase of oleic acid (C18:1?9). The amount of unsaturated fatty acids was inversely proportional to temperature, demonstrating physiological adaptations to increase membrane fluidity. This data will improve prediction of fatty acid characteristics and yields relevant to biofuel production. Keywords: algae; biofuels; climate; fatty acid; Nannochloropsis salina