Effect of bleaching on bioenergetic metabolism and mitochondrial translation of aerobically grown Euglena gracilis

Abstract Unicellular flagellate Euglena gracilis possesses two DNA containing organelles with endosymbiotic origin, mitochondria and chloroplasts. In contrast to mitochondrial DNA, the plastid genome can be partially or completely eliminated by treating cells with different physical or chemical agents. This process is called bleaching, because it leads to the irreversible loss of photosynthesis and thus the permanent loss of green color. Stable bleached mutants are useful models for studying mitochondrial metabolism without the interference with plastid metabolic pathways. We have evaluated the possible impact of permanent bleaching on the function of mitochondria by testing their metabolic capacity and by monitoring mitochondrial translation in aerobically grown bleached strains. We compared the activities of enzymes involved in tricarboxylic acid cycle and oxidative phosphorylation, and the level of oxygen consumption in two green wild type E. gracilis strains and their three stable bleached mutants. We also performed mitochondrial in organello translation in all tested strains and accomplished proteomic analyses of their mitochondrial ATP synthase. Our results suggest that bleaching has no apparent impact on mitochondrial metabolism and translation.