Dynamics of chlorophyll and paramylon accumulation in Euglena gracilis cells at mixotrophic cultivation

Abstract

Microalgae E. gracilis is capable of using ethanol as a carbon and energy source for growth both in the light and in the dark. Ethanol is efficiently utilized under illumination of the culture. At mixotrophic cultivation, the dynamics of accumulation of chlorophyll and paramylon – the main reserve polysaccharide of E. gracilis, was significantly different from the autotrophic control. Chlorophyll content in the mixotrophic cells at moderate intensities of light (100–250 µmol∙m-2 ·s-1) at the beginning of the exponential growth phase decreased and then increased steadily to reach a stationary growth phase. On the contrary, the content of paramylon, was maximal at the lag phase, and decreased in an exponential growth phase. Thus, the synthesis of photosynthetic pigment-containing complexes was delayed at the beginning of cultivation, in the presence of ethanol, and cell growth was mainly due to the substrate uptake. Probably, after assimilation of exogenous ethanol, the observed intensive growth of the culture was provided by the photosynthetic conversion of light energy and usage of carbon deposited in paramylon.

Keywords

• Euglena gracilis
• mixotrophic cultivation
• ethanol
• chlorophyll
• paramylon