Genetic evidence for a mitochondriate ancestry in the 'amitochondriate' flagellate Trimastix pyriformis.
Most modern eukaryotes diverged from a common ancestor that contained the alpha-proteobacterial endosymbiont that gave rise to mitochondria. The 'amitochondriate' anaerobic protist parasites that have been studied to date, such as Giardia and Trichomonas harbor mitochondrion-related organelles, such as mitosomes or hydrogenosomes. Yet there is one remaining group of mitochondrion-lacking flagellates known as the Preaxostyla that could represent a primitive 'pre-mitochondrial' lineage of eukaryotes. To test this hypothesis, we conducted an expressed sequence tag (EST) survey on the preaxostylid flagellate Trimastix pyriformis, a poorly-studied free-living anaerobe. Among the ESTs we detected 19 proteins that, in other eukaryotes, typically function in mitochondria, hydrogenosomes or mitosomes, 12 of which are found exclusively within these organelles. Interestingly, one of the proteins, aconitase, functions in the tricarboxylic acid cycle typical of aerobic mitochondria, whereas others, such as pyruvate:ferredoxin oxidoreductase and [FeFe] hydrogenase, are characteristic of anaerobic hydrogenosomes. Since Trimastix retains genetic evidence of a mitochondriate ancestry, we can now say definitively that all known living eukaryote lineages descend from a common ancestor that had mitochondria.
Hampl
Vladimir
V
Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada.
Silberman
Jeffrey D
JD
Stechmann
Alexandra
A
Diaz-Triviño
Sara
S
Johnson
Patricia J
PJ
Roger
Andrew J
AJ
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D004272:DNA, Mitochondrial / Q000235:genetics*; D004734:Energy Metabolism; D056890:Eukaryota / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D020224:Expressed Sequence Tags; D008969:Molecular Sequence Data; D010802:Phylogeny; D021381:Protein Transport; D017386:Sequence Homology, Amino Acid
D000596:Amino Acids; D004272:DNA, Mitochondrial