Current Biology
Volume 7, Issue 12, 1 December 1997, Pages 995-998
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A mitochondrial Hsp70 orthologue in Vairimorpha necatrix: molecular evidence that microsporidia once contained mitochondria

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Abstract

Microsporidia are small (1–20 μm) obligate intracellular parasites of a variety of eukaryotes, and they are serious opportunistic pathogens of immunocompromised patients [1]. Microsporidia are often assigned to the first branch in gene trees of eukaryotes [2], [3], and are reported to lack mitochondria [2], [4]. Like diplomonads and trichomonads, microsporidia are hypothesised to have diverged from the main eukaryotic stock prior to the event that led to the mitochondrion endosymbiosis [2], [4]. They have thus assumed importance as putative relics of premitochondrion eukaryote evolution. Recent data have now revealed that diplomonads and trichomonads contain genes that probably originated from the mitochondrion endosymbiont [5], [6], [7], [8], [9], leaving microsporidia as chief candidates for an extant primitively amitochondriate eukaryote group. We have now identified a gene in the microsporidium Vairimorpha necatrix that appears to be orthologous to the eukaryotic (symbiont-derived) Hsp70 gene, the protein product of which normally functions in mitochondria. The simplest interpretation of our data is that microporidia have lost mitochondria while retaining genetic evidence of their past presence. This strongly suggests that microsporidia are not primitively amitochondriate and makes feasible an evolutionary scenario whereby all extant eukaryotes share a common ancestor which contained mitochondria.

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RP Hirt, B Healy and TM Embley, Department of Zoology, The Natural History Museum, London SW7 5BD, UK.

CR Vossbrinck, Department of Soil and Water, Connecticut Agricultural Experiment Station, New Haven, Connecticut 06504, USA.

EU Canning, Department of Biology, Imperial College of Science, Technology and Medicine, London SW7 2AZ, UK.

E-mail address for TM Embley (corresponding author): [email protected].