Optimisation of T-ISO biomass production rich in essential fatty acids. II. Effect of different light regimes on the production of fatty acids

It is well documented that culture conditions affect the fatty acid content of microalgae. We report in this study the fatty acid profiles and n-3 HUFA productivity of T-ISO, a popular haptophyte in the aquaculture industry, cultured under three photoperiods (24:0, 16:08 and 12:12 h L:D) combined with three photon flux densities (PFD: 120, 220 and 460 micromol photon m(-2) s(-1)), at 25 degrees C. Sampling took place in both the exponential and post-exponential (light-limited) phase. In general, fatty acid proportions were effected by a strong interaction of L:D x PFD resulting in metabolic changes difficult to be modelled. At the 12:12 and 24:0 h L:D the fatty acid pattern can be summarised as PUFA>SAFA>MUFA, while at 16:08 h L:D as SAFA>PUFA>MUFA reflecting a differential acclimation of the strain under light-dark cycles. At the 12:12 h L:D the PUFA content of biomass was significantly higher than at the other photocycles. PUFA content differences were located in the n-3 fraction with the n-6 content being rather constant. The n-3/n-6 and DHA/EPA ratios under 24:0 h or 12:12 h L:D were optimal according to the literature for fish and shellfish nutrition requirements. In contrast, the 16:08 h L:D regimes, especially at low PFD, produced inadequate ratios. The production of n-3 HUFA in T-ISO is essentially influenced by the total photon flux available per day in a similar manner with growth. The capacity of the strain for storing lipid is limited under the conditions tested; consequently, the fatty acid content follows the biomass yield and productivity pattern. Hence, in the context of aquaculture a light regime of 12:12 h L:D and a PFD within the photolimitation-photoinhibition range offers advantages for the culture of T-ISO. If the high investment could be substantiated, continuous cultures under 24:0 h L:D at the same PFD range could serve as an optimisation basis using advanced photobioreactors.