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Multiple origins of anaerobic ciliates with hydrogenosomes within the radiation of aerobic ciliates

Lookup NU author(s): Emeritus Professor T. Martin Embley FMedSci FRSORCiD, Professor Robert HirtORCiD


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Some ciliates live anaerobically and lack mitochondria, but possess hydrogenosomes: organelles that contain hydrogenase and produce hydrogen. The origin of hydrogenosomes has been explained by two competing hypotheses: (i) they are biochemically modified mitochondria; or (ii) they are derived from endosymbiotic association(s) of ciliates and anaerobic eubacteria that possessed the hydrogenosome biochemistry. Phylogenetic analyses of representative aerobic, and anaerobic hydrogenosomal ciliates using host nuclear SSU rDNA sequences indicate a minimum of three, but more likely four, separate origins of hydrogenosomes. Whereas this does not refute either hypothesis, the implausibility of multiple convergent endosymbioses gives further support to the view that hydrogenosomes in ciliates derive from an existing organelle, which ultrastructural evidence suggests is the mitochondrion. Our results indicate a considerable potential for physiological-biochemical plasticity among a group of predominantly aerobic eucaryotes, and provide a phylogenetic framework to further refine and test hypotheses of the origins of the hydrogenosomal enzymes.

Publication metadata

Author(s): Embley TM; Hirt RP; Finlay BJ; Dyal PL; Wilkinson M; Williams AG

Publication type: Article

Publication status: Published

Journal: Proceedings of the Royal Society B: Biological Sciences

Year: 1995

Volume: 262

Issue: 1363

Pages: 87-93

Print publication date: 23/10/1995

ISSN (print): 0962-8452

ISSN (electronic): 1471-2954

Publisher: The Royal Society Publishing


DOI: 10.1098/rspb.1995.0180


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