Culture of Euglena gracilis in photoautotrophy for paramylon production: effect of pH and media composition

Abstract

Microalgae have been widely studied in biotechnology for their application in various areas such as bioremediation, production of biofuels, or use in nutrition. More specifically, certain species are recognized to produce compounds of high commercial value. Euglena is a group of microalgae characterized by the generation of the reserve polysaccharide paramylon, with promising prospects for its application in pharmacology, nutrition, to produce bioplastics, or biodiesel. Paramylon is accumulated mainly in the presence of organic carbon in the culture medium; however, this represents a challenge when establishing a large-scale culture due to the risk of biological contamination. In this study, an extensive study of the literature was carried out with respect to the autotrophic culture of Euglena gracilis destined to paramylon production. As a result, we evaluated the effect of culture pH, vitamin supplementation, and nitrogen source in the culture medium in order to reach the maximum biomass productivity. A pH of 7.5 and ammonium as nitrogen source were optimum for the autotrophic culture of E. gracilis, while an improvement in productivity was not observed with vitamin supplementation. Finally, it was possible to scale up the photoautotrophic culture of E. gracilis to a 1-L airlift photobioreactor. In conclusion, there is still much optimization work to achieve the biomass and paramylon productivity reported for the heterotrophic cultures of E. gracilis, but the results of this study reveal its viability.