Taxonomy and growth conditions concur to determine the energetic suitability of algal fatty acid complements

Abstract

We hypothesize that, in algae, carbon allocation to lipids depends on the combined effects of the metabolic constraints imposed by the genotype (i.e., species-specific differences in composition) and on the acclimation responses (phenotype) to changes in the stoichiometry of available inorganic carbon (for photosynthesis) and nitrogen (primarily for amino acids, protein, and nucleic acid synthesis). We thus cultured three taxonomically distinct algae, the green alga Dunaliella salina, the diatom Thalassiosira pseudonana, and the dinoflagellate Protoceratium reticulatum, at four nitrate concentrations and constant inorganic carbon. Since energy availability also directly impacts carbon partitioning, we studied the effect of irradiance on the oil quality of P. reticulatum. We used Fourier transform infrared (FTIR) spectroscopy to study carbon allocation and biomass reduction level and gas chromatography for fatty acid analysis. The fatty acid complements of the three species were different; within each species, growth conditions substantially altered oil quality. We ranked the oils in terms of their suitability as biodiesels, using international standards as reference. We believe that this approach may help to identify the appropriate combination of taxa and culture conditions for algal biodiesel production and in general offers insight on carbon allocation to fatty acids.