Mitochondrion-Related Organelles in Eukaryotic Protists

The discovery of mitochondrion-type genes in organisms thought to lack mitochondria led to the demonstration that hydrogenosomes share a common ancestry with mitochondria, as well as the discovery of mitosomes in multiple eukaryotic lineages. No examples of examined eukaryotes lacking a mitochondrion-related organelle exist, implying that the endosymbiont that gave rise to the mitochondrion was present in the first eukaryote. These organelles, known as hydrogenosomes, mitosomes, or mitochondrion-like organelles, are typically reduced, both structurally and biochemically, relative to classical mitochondria. However, despite their diversification and adaptation to different niches, all appear to play a role in Fe-S cluster assembly, as observed for mitochondria. Although evidence supports the use of common protein targeting mechanisms in the biogenesis of these diverse organelles, divergent features are also apparent. This review examines the metabolism and biogenesis of these organelles in divergent unicellular microbes, with a focus on parasitic protists.