The use of multi-parameter flow cytometry to study the impact of n-dodecane additions to marine dinoflagellate microalga Crypthecodinium cohnii batch fermentations and DHA production.

The physiological response of Crypthecodinium cohnii batch cultivations and docosahexaenoic acid (DHA) production to n-dodecane additions were studied. Different n-dodecane concentrations [0, 0.5, 1, 2.5, 5, 10 and 20% (v/v)] were added to preliminary shake flask cultivations. The n-dodecane fraction that gave best results in terms of biomass and DHA production was 0.5% (v/v). The n-dodecane fractions of 2.5, 5, 10 and 20% (v/v) to C. cohnii preliminary shake flask cultures inhibited the microalgal growth and DHA production, although a high proportion of cells with intact cytoplasmic membrane was present in the end of these fermentations. After the addition of a pulse of n-dodecane (0.5% v/v) to C. cohnii exponential growing cells in a bioreactor, glucose uptake volumetric rate increased 2.5-fold, while biomass production volumetric rate increased 2.8-fold. The specific growth rate was increased 1.5-fold. The DHA % in biomass, DHA % of TFA and DHA concentration also increased (54, 22 and 58%, respectively), after the n-dodecane addition. At this n-dodecane fraction (0.5% v/v), multi-parameter flow cytometry demonstrated that C. cohnii cell membrane integrity was not affected. The results demonstrated that the addition of 0.5% of n-dodecane (v/v) to C. cohnii fermentations can be an easy and cheap way for enhancing the biomass and DHA production, avoiding the use of high speed rates (resulting in important power agitation costs) that affects the microalga proliferation and increases the bioprocess costs. A new strategy to improve the DHA production from this microalga in two-phase large-scale bioreactors is now in progress.