The Origins of Mitochondria, Mitosomes and Hydrogenosomes

From the foregoing section it should be clear that there is vast diversity in the structure, function and evolutionary history of mitochondrion-derived organelles in anaerobic protists. Although much has yet to be learned about these disparate organellar systems, several evolutionary scenarios regarding their evolutionary history seem possible. The two most likely scenarios are shown in Fig. 10.5 and are discussed next. 

it is possible that enzymes of aerobic and anaerobic energy metabolism found in mitochondrion-related organelles of present-day eukaryotes originated with the a-proteobacterial symbiont that gave rise to mitochondria (Fig. 10.5, top), which could have been a facultative aerobe (e.g. Martin and Muller 1998 and Rotte et al. 2000 provide a biochemical rationale for this view). After the initial symbiotic integration of the mitochondrial ancestor, many endosymbiont genes were transferred to the nucleus, some of which were 

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