Hydrogenosome

Hydrogenosomes were isolated, purified, biochemically characterized and named in 1973 by Donald Gustav Lindmark and Miklós Müller at the Rockefeller University. In addition to this discovery of novel organelle, they also demonstrated for the first time the presence of pyruvate:ferredoxin oxido-reductase and hydrogenase in eukaryotes. Since their discovery, hydrogenosomes have been found in a variety of anaerobic unicellular ciliates, flagellates, and fungi. The most notable amongst these is the parasitic Trichomonas vaginalis. In 2010, new species of microscopic animals in the phylum Loricifera, such as species of Rugiloricus species and Pliciloricus which known for the first time as animals (metazoans) capable of living exclusively in oxygenless conditions. They contain hydrogenosome-like organelles by which they produce energy (ATP) by metabolizing hydrogen deep in the Mediterranean sediments. Other new species subsequently discovered such as Spinoloricus cinziae also contained the same organelle. == Description ==

Hydrogenosomes are organelles that are speculated to have evolved from mitochondria to provide a different mechanism for anaerobic ATP synthesis utilizing pyruvate. The reaction results in the production of molecular hydrogen, from which the organelle receives its name. However, a hydrogenosomal genome has been detected in the cockroach ciliate Nyctotherus ovalis, and the stramenopile Blastocystis. Due to the fact that many organisms have evolved to fit their anaerobic environments, a multitude of organisms have independently evolved hydrogenosomes or structures with similar functions. The similarity between Nyctotherus and Blastocystis, which are only distantly related, is believed to be the result of convergent evolution, and calls into question whether there is a clear-cut distinction between mitochondria, hydrogenosomes, and mitosomes (another kind of degenerate mitochondria). == Source organisms ==

hydrogenosome: pyruvate (PYR) is turned into carbon dioxide (CO2) and acetate while producing molecular hydrogen (H2) and converting ADP into ATPHydrogenosomes are present in different organisms across three kingdoms such as Protista, Fungi and Animalia. The vast variety of source organisms can be accredited to the theorized convergent evolution of hydrogenosomes from mitochondria to fit an anaerobic environment. Some of the best understood organisms are: Protists • Parabasalid flagellates like Trichomonas vaginalis, Tritrichomonas foetus, Histomonas meleagridis. • Preaxostylid flagellates like Trimastix pyriformis. • Heterolobosean amoeboflagellates likePsalteriomonas lanterna. • Anaerobic ciliates like Nyctotherus ovalis, Metopus palaeformis, Trimyema compressum, Caenomorpha uniserialis, Dasytricha ruminantium. Fungi • Anaerobic chytridiomycetes including species of Neocallimastix and Piromyces. Animals • Species of the phylum Loricifera, like Spinoloricus cinziae, Rugiloricus species and Pliciloricus species. == ATP synthesis ==

The hydrogenosomes of trichomonads (the most studied of the hydrogenosome-containing microorganisms) produce molecular hydrogen, acetate, carbon dioxide and ATP by the combined actions of pyruvate:ferredoxin oxido-reductase, hydrogenase, acetate:succinate CoA transferase and succinate thiokinase. Superoxide dismutase, malate dehydrogenase (decarboxylating), ferredoxin, adenylate kinase and NADH:ferredoxin oxido-reductase are also localized in the hydrogenosome. == See also ==