Taxonomy and growth conditions concur to determine the energetic suitability of algal fatty acid complements Mario Giordano & Matteo Palmucci & Alessandra Norici Received: 21 July 2014 /Revised and accepted: 30 October 2014 # Springer Science+Business Media Dordrecht 2014 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 inor- ganic 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 ni- trate concentrations and constant inorganic carbon. Since en- ergy 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 reduc- tion 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 be- lieve 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. Keywords Algae . Biodiesel . C allocation . Cell composition . Elemental stoichiometry . Fatty acids . Phytoplankton Introduction Microalgae constitute a very promising feedstock for the production of oils to be used as fuel (Pandey et al. 2014). In addition to their substantial (although highly variable) oleogenic capacity, their potential as source of biofuel is associated to the fact that they can be cultivated in marginal lands or on wastewater, with minimal (if any) competition with key crops. Microalgae, therefore, fit the definition of sources of “second-generation biofuels” (Schenk et al. 2008). It should be mentioned, however, that the cost of algal biofuel production is presently not competitive with that of fossil fuels (Sun et al. 2011), although technological improve- ments and the unavoidable increase of fossil fuel price may change this in the future. In the short term, economical via- bility of algal biofuel productions appears to depend on mul- tiple use of the biomass (Sun et al. 2011). Because of the general interest in this topic, extensive (although still very limited in relation to the number of known algal species) screening has been conduced to identify the most oleogenic algal species and strains (e.g., Griffiths and Harrison 2009; Palmucci and Giordano 2012; Picardo et al. 2013 and references therein). The results of these studies suggest that special attention must be devoted to the study of the impact of culture conditions on oleogenesis, since microalgae carbon partitioning varies greatly in response to environmental perturbations. It should be noted, however, that the extent by which algae acclimate to changes in the external milieu are very species-specific and, while some algae promptly respond to even moderate changes of their growth environment, others are capable of maintaining compositional homeostasis in spite of substantial external changes (Giordano 2013). It is generally accepted that oil production in microalgae is enhanced by nutrient, especially nitrogen, limitation. This is due to the fact that nitrogen shortage stimulates the allocation M. Giordano (*) : M. Palmucci : A. Norici Dipartimento di Scienze della Vita e dell’Ambiente, Università Politecnica delle Marche, Via Brecce Bianche, 60131 Ancona, Italy e-mail: m.giordano@univpm.it M. Giordano Institute of Microbiology ASCR, Algatech, Trebon 37981, Czech Republic J Appl Phycol DOI 10.1007/s10811-014-0457-5