The Blastocystis mitochondrion-like organelles

The organelles in Blastocystis that resemble mitochondria are an enigma as the organism is a strict anaerobe. Recent sequence analyses of the organelle genome and over 12,000 expressed sequence tags (ESTs) has given us many insights into the role these organelles play in the metabolism of the cell. The genome encodes several subunits of NADH dehydrogenase (complex I) but lacks all trace of genes for cytochrome and ATPase subunits (Complexes III-V). ESTs confirm the presence of complexes I and II, and indicate that this partial electron transport chain may lead to an alternative oxidase. The ESTs also suggest that many other metabolic pathways characteristic of mitochondria are still present in the Blastocystis organelles. However, other findings show that the organelle also has characteristics in common with hydrogenosomes, as a gene encoding [FeFe] hydrogenase is present and the protein has been localised to the organelles. The nuclear genome should clarify many of the remaining questions surrounding these unusual organelles.