Optimization of complex medium composition for heterotrophic cultivation of Euglena gracilis and paramylon production

In this research heterotrophic cultivation of photosynthetic protist Euglena gracilis was carried out on synthetic (Hutner medium) and complex cultivation media in order to produce -1, 3-glucan (paramylon). For preparation of complex media various industrial by-products (e.g. molasses, corn steep solid, yeast and beef extract) with or without addition of pure compounds [glucose, galactose, fructose, lactose, maltose, sucrose and (NH4)2HPO4] were used. Heterotrophic cultivation of E. gracilis was performed in Erlenmeyer flasks and additionally confirmed during research in the stirred tank bioreactor. The results of this research clearly show that E. gracilis could easily metabolize glucose and fructose (compared to other sugars used in this research) as carbon sources and corn steep solid as complex nitrogen and growth factors source for biomass growth and paramylon synthesis during cultivation in heterotrophic conditions. Furthermore, it was also proved that addition of (NH4)2HPO4 (source of nitrogen and phosphorus), beef extract (source of nitrogen compounds and vitamin B12) or gibberellic acid (plant growth hormone) did not have significant impact on the biomass growth and paramylon synthesis. After optimization of complex medium composition and verification of these results during E. gracilis cultivations in the stirred tank bioreactor it was concluded that medium composed of glucose (20 g/L) and corn steep solid (25 g/L) is the most suitable complex cultivation medium for industrial production of paramylon.