Selenium incorporation to amino acids in Chlorella cultures grown in phototrophic and heterotrophic regime

Microalgae accumulate bioavailable selenium containing amino acids (Se-AAs) and these are useful as a food supplement. While this accumulation has been studied in phototrophic algal cultures, little data exists for heterotrophic cultures. We have determined Se-AAs content, selenium/sulphur (Se/S) substitution rates and overall Se accumulation balance in photo- and heterotrophic Chlorella cultures. Laboratory trials revealed that heterotrophic cultures tolerate Se doses ~8-fold higher compared to phototrophic cultures, resulting in a ~2-3-fold higher Se-AAs content. In large-scale experiments both cultivation regimes provided comparable Se-AAs content. Outdoor phototrophic cultures accumulated up to 400 μg g-1 of total Se-AAs and exhibited a high level of Se/S substitution (5-10%) with 30-60% organic/total Se embedded in the biomass. A slightly higher content of Se-AAs and ratio of Se/S substitution was obtained for a heterotrophic culture in pilot-scale fermentors. The data presented here shows that heter...