Metabolic flux analysis in Euglena gracilis

In this study, 13C metabolic flux analysis and flux balance analysis are used to investigate the metabolic phenotypes of Euglena gracilis grown on glucose, acetate, ethanol and pyruvate. A set of metabolic flux maps of E. gracilis are presented. These flux maps emphasise the limited contribution of plastidic metabolic processes and the oxidative pentose phosphate pathway in heterotrophic metabolism of E. gracilis. Comparison of the flux maps of wild-type and aplastidic E. gracilis on glucose reveals that disruption of chloroplast increases demand for the cofactors required for cell maintenance, resulting in higher fluxes through the central pathways of carbohydrate oxidation and a decrease in carbon conversion efficiency in aplastidic cells. Moreover, flux maps of E. gracilis on different respiratory substrates emphasise the importance of the glyoxylate shunt and malate dehydrogenase in supporting anaplerosis when grown on acetate and ethanol, but not on pyruvate in which the precursor for gluconeogenesis is mainly provided by pyruvate carboxylase. The flux maps reported in this study reveal the impact of chloroplast disruption on the metabolic phenotype of Euglena and provide new insights into the metabolism of substrates differing in carbon composition and chemical redox potential