Towards the biorefinery concept: Interaction of light, temperature and nitrogen for optimizing the co-production of high-value compounds in Porphyridium purpureum

Abstract

The interactive effects of light, temperature and nitrogen regime on phycobiliprotein (PB) production and other compounds such as fatty acids, pigments and carbohydrates, were studied during batch-cultivation of Porphyridium purpureum, a red microalga, containing multiple compounds of commercial interest. Results indicate that nitrogen-replete modes, such as semi-continuous or continuous regime represent the most suitable culture strategy for PB, carbohydrate, total fatty acid (TFA) and eicosapentaenoic acid (EPA) production in P. purpureum. Nitrate-deficiency causes a strong decrease in growth performance, as well as in its PE, TFA and EPA contents which may be related to membrane degradation; but induces carbohydrate accumulation. Nitrate-starved cells of P. purpureum had the ability to restore PB and TFA contents, and specifically phycoerythrin (PE) and EPA levels, after medium refreshment, suggesting an almost complete regeneration of the plastidic membranes and phycobilisomes. Using response surface methodology (RSM), our results highlight for the first time the optimally combined light and temperature conditions necessary to promote growth and compound production, in particular PB, in P. purpureum batch-cultivated in nitrogen-replete medium. A simultaneous increase in light and temperature causes a strong decrease in cellular PB, TFA, EPA and pigment contents, suggesting a severe damage and possible disruption of thylakoid membranes. The highest PB content (~2.9% d.w.) was reached under combined low light (30μmolm−2s−1) and low temperature (10°C). Despite of this, maximal PB productivity was obtained at 20°C and under low light intensity, reaching up to 33.3mgL−1 (~2%d.w.). Under such specific growth conditions, P. purpureum biomass also contained substantial amounts of other valuable products (i.e., carbohydrates, EPA, Chl. a, zeaxanthin, β-carotene) which could therefore be co-extracted, with PB, by applying a biorefinery approach.