Evolution of hydrogenosomes: adaptation of free living protists Mastagamoeba balamuthi and Naegleria gruberi to oxygen-poor environment

Various protists from different eukaryotic groups are able to live in the oxygen-poor niches. Their metabolic adaptation to anaerobiosis is usually associated with loss of the typical mitochondrial functions, including the tricarboxylic acid cycle and oxidative phosphorylation. Anaerobic forms of mitochondria generate ATP exclusively by the substrate level phosphorylation in the hydrogen-producing hydrogenosomes, or the ATP synthesis is completely lost as observed in mitosomes. Consequently, the proteomes of such organelles are considerably reduced. It is a question of debate whether the anaerobic forms of mitochondria evolved directly from premitochondrial organelles that might be present in ancient anaerobic eukaryotes or during the secondary adaptation of aerobic eukaryotes to anaerobic niches. The protist from super group Amoebozoa, Mastigamoeba balamuthi, is very attractive for study of mitochondria evolution, because it is closely related with two very different organisms: (i) the aerobic, free-living slime molds such as Dictyostelium that possesses classical aerobic mitochondria, as well as (ii) the anaerobic parasite Entamoeba histolytica that contains mitosomes, the most reduced form of mitochondria. The mitochondria derived organelles in anaerobic, free-living M. balamuthi could represent..