The Mitochondrion-Related Organelles of Blastocystis

Blastocystis is an anaerobic microbial eukaryote that inhabits the gut of various animals. While it was considered to be a parasite, its pathogenicity is controversial, since recent estimations suggest that Blastocystis could be present in more than one billion humans. Blastocystis belongs to the stramenopiles (heterokonts), a diverse group of eukaryotes that also include unicellular diatoms and giant multicellular kelps. The Blastocystis cell lacks typical features of other stramenopiles, its genome has laterally acquired many genes from other prokaryotes and eukaryotes, resulting in having exceptional biochemistry and unique adaptations of its mitochondria. For example, Blastocystis mitochondrion-related organelles (MROs) have characteristics of typical mitochondria, including Complex I and II from electron transport chain, mitochondrial DNA, Fe-S cluster assembly and amino acid metabolism, but also proteins that are typically present in obligate anaerobes including FeFe-Hydrogenase, pyruvate metabolism and alternative oxidase. Some of the pathways have been localized and biochemically characterized, providing a better understanding on the functions of these organelles. In this chapter, we will present and examine the status quo regarding the biology and morphology of Blastocystis MROs and we will discuss future avenues on exploring even further adaptations of these organelles.