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Molecular data suggest an early acquisition of the mitochondrion endosymbiont

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


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The three deepest branching eucaryotic lineages in small subunit ribosomal RNA phylogenies are the amitochondriate Microspora, Metamonada and Parabasala. They are followed by either the Euglenozoa (e.g. Euglena and Trypanosoma) or the Percolozoa as the first mitochondria-containing eucaryotes. To investigate the hypothesis of an even earlier timing of the mitochondrion endosymbiosis we have amplified a partial cpn-60 coding region from the parabasalid Trichomonas vaginalis and the first such sequence from a percolozoan, Naegleria fowleri. Analysis of predicted protein sequences reveals a high degree of sequence similarity (> or = 40%) with a selection of published bacterial and mitochondrial cpn-60s for both taxa. Both sequences were recovered within a strongly supported monophyletic group, otherwise defined by mitochondrial sequences, which systematically clustered with alpha-proteobacteria. These results provide compelling evidence that the ancestor of T. vaginalis once contained the endosymbiont which gave rise to mitochondria, and suggest that this symbiosis probably occurred before the Trichomonas lineage diverged from the main eukaryote trunk. It also makes feasible the published hypothesis that the Trichomonas hydrogenosome might represent a biochemically modified mitochondrion. Analysis of the N. fowleri cpn-60 did not support the hypothesis that the mitochondrion-containing Percolozoa represent an earlier branch in the cpn-60 tree than Trichomonas or Trypanosoma.

Publication metadata

Author(s): Embley TM; Hirt RP; Horner DS; Kilvington S; Lloyd D

Publication type: Article

Publication status: Published

Journal: Proceedings of the Royal Society B: Biological Sciences

Year: 1996

Volume: 263

Issue: 1373

Pages: 1053-1059

Print publication date: 22/08/2011

ISSN (print): 0962-8452

ISSN (electronic): 1471-2954

Publisher: The Royal Society Publishing


DOI: 10.1098/rspb.1996.0155


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