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The Microsporidia, also known as Microspora, are a monophyletic phylum of tiny eukaryotic parasites. Growth and reproduction can occur only within host cells. Early research on the ribosomal genes of Microsporidia placed them at the base of the eukaryote evolutionary tree with other 'primitive' amitochondriate protozoans (Keeling and Fast 2002). Subsequent analyses of a variety of genes using more sophisticated methods have indicated that Microsporidia are close to the fungi. Molecular evidence for the relationship between Microsporidia and fungi is supported by biochemical and developmental features of the group (Keeling 2003). Studies on mitochondrial proteins (including HspT0) have indicated that typical mitochondria have been secondarily lost, although remnants in the form of small membrane-bound organelles have been detected (Williams et al. 2002). Parsimonious features of the Microsporidia, including small genome size, prokaryote-like ribosomal genes and the loss of typical eukaryotic organelles are thought to be associated with the highly specialised lifestyle of these parasites (Mathis 2000, Weiss 2000). |
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