Growth and docosahexaenoic acid production performance of the heterotrophic marine microalgae Crypthecodinium cohnii in the wave-mixed single-use reactor CELL-tainer

The process development of docosahexaenoic acid (DHA) with the heterotrophic marine microalgae Crypthecodinium cohnii is challenging, since the oxygen demand of the cells is high and the cell itself sensitive to high shear forces. Furthermore, the marine medium, which comprises a high salt concentration, accelerates corrosion of steel typically applied in bioreactors. Single-use bioreactors (SUBs) provide an alternative to common stainless steel stirred tank reactors (STR) for the development of bioprocesses with marine microorganisms, when the development stage does not allow for the application of special steel or the replacement of chloride ions in the medium. Among the readily-available SUBs, the CELL-tainer exhibits outstanding high oxygen transfer rates. A direct comparison of this SUB with a standard stirred tank bioreactor (STR) was performed for the cultivation of C. cohnii. The biomass and DHA concentrations were similar in both devices, while the biomass yield coefficient, related to the glucose consumption, was reduced by 35% and the DHA yield coefficient by 21% in the STR. The impact of shear stress on cell physiology was elucidated by flow cytometry, revealing a five times higher amount of cell debris in the STR and 14 times higher amount of cells with a low cell membrane potential as evaluated by bis-(1,3-dibutylbarbituric acid) trimethine oxonol staining. Foam and biofilm formation, which is a problem in the STR, did not occur in the SUB. The study underlines that the CELL-tainer can replace the STR, ensuring sufficient oxygen transfer rates and decreasing cell damage and foam formation.