Organisms Without Mitochondria, How It May Happen?
Decades of investigations have clearly shown that protists living in low-oxygen environments possess mitochondria despite their textbook function, oxidative phosphorylation, is usually absent. The presence of these, in some cases, very rudimental mitochondria has been ascribed to their irreplaceable role in the synthesis of FeS clusters, prosthetic groups of several essential proteins. The deep investigation of the oxymonad Monocercomonoides exilis (Preaxostyla, Metamonada) revealed that this organism very likely represents a notable exception, in which the synthesis of FeS clusters runs in the cytosol and mitochondrion is absent. Investigation of a broader spectrum of oxymonads and their relatives provided evidence that the profound reorganisation of FeS cluster synthesis was initiated by a HGT of the bacterial pathway SUF and a loss of the mitochondrial pathway ISC already before the last common ancestor of this clade. This innovation was very likely a preadaptation for (and not a consequence of) the mitochondrial loss, which happened much later and only in the oxymonad lineage. M. exilis and other oxymonads are being further studied because they represent valuable examples relevant to our understanding of the reductive evolution of organelles and to the origin of the eukaryotic cell.
The salary of VH was funded from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 771592), from the Centre for research of pathogenicity and virulence of parasites reg. nr.: CZ.02.1.01/0.0/0.0/16_019/0000759, from the Ministry of Education, Youth and Sports of CR within the National Sustainability Program II (Project BIOCEV-FAR) LQ1604 and from the project ‘BIOCEV’ (CZ.1.05/1.1.00/02.0109).
- Hampl V (2016) Preaxostyla. In: Handbook of the protists. Springer, Cham, pp 1–36Google Scholar
- Leander BS, Keeling PJ (2004) Symbiotic innovation in the oxymonad Streblomastix strix. J Eukaryot Microbiol 51:291–300. https://doi.org/10.1111/j.1550-7408.2004.tb00569.x CrossRefPubMedGoogle Scholar
- Noda S, Inoue T, Hongoh Y et al (2006) Identification and characterization of ectosymbionts of distinct lineages in Bacteroidales attached to flagellated protists in the gut of termites and a wood-feeding cockroach. Environ Microbiol 8:11–20. https://doi.org/10.1111/j.1462-2920.2005.00860.x CrossRefPubMedGoogle Scholar
- Treitli SC, Kotyk M, Yubuki N, Jirounková E, Vlasáková J, Smejkalová P, Šípek P, Čepička I, Hampl V (2018) Molecular and morphological diversity of the oxymonad genera Monocercomonoides and Blattamonas gen. nov. Protist 169(5):744–783. https://doi.org/10.1016/j.protis.2018.06.005 CrossRefPubMedGoogle Scholar
- Vacek V, Novák LVF, Treitli SC et al (2018) Fe-S cluster assembly in oxymonads and related protists. Mol Biol Evol. https://doi.org/10.1093/molbev/msy168
- Zhang Q, Táborský P, Silberman JD et al (2015) Marine isolates of Trimastix marina form a plesiomorphic deep-branching lineage within Preaxostyla, separate from other known trimastigids (Paratrimastix n. Gen.). Protist 166:468–491. https://doi.org/10.1016/j.protis.2015.07.003 CrossRefPubMedGoogle Scholar