Amino acid excretion from Euglena gracilis cells in dark and anaerobic conditions

Abstract

Euglena gracilis is a unicellular, eukaryotic alga, and is commercially used for production of food, medication, cosmetics, and dietary supplements. The algal cells are known to produce wax ester and succinate under dark and anaerobic conditions. In our study, we analysed a range of metabolites, and observed the excretion of various amino acids by E. gracilis cells. Arginine, alanine, leucine, lysine, and valine were excreted in amounts exceeding 30 mg/L into the culture medium upon anaerobic incubation for three days. Furthermore, an increase in the concentration of (NH4)2HPO4 affected the production of amino acids differently: those amino acids synthesized from glycolysis metabolites decreased, whereas those synthesized from tricarboxylic acid cycle metabolites increased with an increase in (NH4)2HPO4. Glutamate excretion was uniquely regulated by (NH4)2HPO4 concentration. Moreover, we found that the production of glutamate was regulated by the pH of the culture medium, but not by nitrogen, phosphate, and salt concentrations. These results demonstrate the ability of E. gracilis to synthesize various amino acids under dark and anaerobic conditions, and contribute valuable information for the commercial and scientific applications of fermentation of eukaryotic algae.