Abstract
Accurate prediction of algal biofuel yield will require empirical determination of physiological responses to the environment, particularly light and temperature. One strain of interest, Nannochloropsis salina, was subjected to ranges of light intensity (5–850 μmol m−2 s−1) and temperature (13–40 °C) and its 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 m−2 s−1. Fatty acids were detected by gas chromatography with flame ionization detection (GC-FID) after transesterification to corresponding fatty acid methyl esters (FAMEs). 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 eicosapentaenoic acids (C20:5ω3). 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 (C18:1ω9). The amount of unsaturated fatty acids was inversely proportional to temperature, demonstrating physiological adaptations to increase membrane fluidity. These data will improve prediction of fatty acid characteristics and yields relevant to biofuel production.
Highlights
Interest in using microalgae biofuels as drop-in replacements for fossil fuels has inspired efforts to increase the rate of lipid production in microalgal cultures [1,2,3]
By making repeated measurements of acclimated, non-self-shading cultures [9] in Roux bottle photobioreactors, at various light intensities, the relationship between μ and I was found to be best approximated by a Monod-type function [10], with μmax = 1.3 day−1 and KI = 37 μmol m−2 s−1 photon flux density (PFD)
Maximum biomass productivity was obtained at the highest light intensity, the most efficient light to biomass conversion [11] was obtained when incident light intensities were between 26 and 55 μmol m−2 s−1
Summary
Interest in using microalgae biofuels as drop-in replacements for fossil fuels has inspired efforts to increase the rate of lipid production in microalgal cultures [1,2,3]. There are two ways to increase areal lipid productivity (mass of lipids per unit of area per unit of time): either increase the rate of biomass accumulation, or increase the proportion of the biomass that contains a useful lipid. To achieve this objective, numerous strategies including nutrient starvation, bioprocess optimization and genetic modification can be used [5]. The potential lipid productivity of a commercial algae cultivation facility will depend on light and temperature, which are obviously determined by location. Lipid productivity is a strain-specific function of physiological responses to many factors, including incident light intensity and cultivation temperature [8]. Presented here is a characterization of one particular strain of interest, Nannochloropsis salina CCMP 1776 under constant illumination and nutrient replete conditions
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