Production of alpha-tocopherol by sequential heterotrophic-photoautotrophic cultivation of Euglena gracilis

Photoautotrophic cultivation of Euglena gracilis results in cells with high a-tocopherol content but the final cell concentration is usually very low due to the difficulty of supplying light efficiently to the photobioreactor . On the other hand, Euglena grows heterotrophically to high cell concentra tions, using various organic carbon sources, but the alpha-tocopherol conte nts of heterotrophically grown cells are usually very low. Sequential heter otrophic/photoautotrophic cultivation, by which cells are grown heterotroph ically to high cell concentrations and then transferred to photoautotrophic culture for accumulation of alpha-tocopherol was therefore investigated fo r efficient alpha-tocopherol production. In batch culture, using glucose as the organic carbon source, the cellular alpha-tocopherol content increased from 120 mu g g(-1) at the end of heterotrophic phase to more than 400 mu g g(-1) at the end of the photoautotrophic phase. By using ethanol as the o rganic carbon source during the heterotrophic phase, adding corn steep liqu or as a nitrogen source and optimizing light supply during the photoautotro phic phase, the alpha-tocopherol content of the cells at the end of the pho toautotrophic phase increased to 1700 mu g g(-1). A system consisting of a mini-jar fermenter (for the heterotrophic phase) and an internally illumina ted photobioreactor (for the photoautotrophic phase) was then constructed f or continuous sequential heterotrophic/photoautotrophic cultivation. The ce lls were continuously cultivated heterotrophically in the mini-jar fermente r and the effluent was continuously passed through the photobioreactor for cr-tocopherol accumulation. In this way, it was possible to produce 7 gl(-1 ) cells containing about 1100 mu g alpha-tocopherol per g-cell continuously for more than 420 h. The continuous process resulted in alpha-tocopherol p roductivity of 100 mu g l(-1) h(-1) which is about 9.5 and 4.6 times higher than those obtained in batch photoautotrophic culture and batch heterotrop hic cultures, respectively. (C) 1999 Elsevier Science B.V. All rights reser ved.