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Scientists Find Gut Microbe That Survives Without Mitochondria (npr.org)
An anonymous reader writes: Scientists have found a eukaryote microbe that completely lacks mitochondria, which are the powerhouses inside eukaryotic cells, the type of cells that make up humans, animals, plants and fungi. All eukaryotic cells contain a nucleus, organelles and mitochondrion. Scientists believe they were once free-living bacteria that got engulfed by primitive, ancient cells that were evolving to become what they are today. Anna Karnkowska, a researcher in evolutionary biology at the University of British Columbia in Vancouver, found a gut microbe that contains no trace that it made any mitochondrial proteins at all. "That should theoretically kill the cell -- it shouldn't exist," she said. The researchers learned that these cells use a kind of machinery that is different than relying on mitochondria to assemble iron-sulfur clusters, which is thought to be a mitochondrial function. Michael Gray, biochemist at Dalhousie University in Halifax, Nova Scotia, calls the discovery of a eukaryote without any vestige of mitochondrion, "unprecedented." He adds, the results do not negate the idea that the acquisition of a mitochondrion was an important and perhaps defining event in the evolution of eukaryotic cells, because this organism's ancestors had mitochondria that were then lost after the cells acquired their non-mitochondrial system for making iron-sulfur clusters.
Mitosomes in Giardia, Entamoeba, and Microsporidia represent the most extreme cases of mitochondrial reduction known to date, and yet they still contain recognizable mitochondrial protein translocases and usually an ISC system. The specific absence of all these mitochondrial proteins in the genome of Monocercomonoides sp. indicates that this eukaryote has dispensed with the mitochondrial compartment completely.