The essential role of mitochondria in the consumption of waste-organic matter and production of metabolites of biotechnological interest in Euglena gracilis

Abstract To assess the role of Euglena gracilis mitochondrial metabolism on the degradation of organic matter present in liquid waste, heterotrophic cells were cultured in the presence of waste supernatants (waste-SN) from eukaryotic (human cancer, human parasite) cell growth media, which are rich in protein and micronutrients, as well as metabolic end-products such as ethanol and glucose. Prior treatment of waste-SN with papain was required to provide free amino acids, which E. gracilis cells actively consumed. Under aerobiosis, biomass production and contents of paramylon, total protein and relevant metabolites were similar for waste-SN, glutamate+malate (GM)- and glucose-grown cells. However, under microaerophilia, fatty acids (potentially useable as biofuels) and alpha-tocopherol contents were higher in waste-SN grown cells. Decreased metabolite contents and cell growth were attained after cell incubation with either azide, oxalate or rotenone. Aminotransferase activities, CO2 production (Krebs cycle), O2-uptake (respiratory chain) and formation of transmembrane electrochemical H+ gradient in isolated mitochondria from waste-SN grown cells were of similar magnitude to those displayed by mitochondria isolated from GM-grown cells. Data indicated that organic matter waste (such as ethanol and amino acids such as glutamate, glutamine and proline) can be oxidized by mitochondria and used as a carbon source for synthesis of vitamin E and other biotechnological relevant metabolites by E. gracilis.