Hypothetical endosymbiont ancestor of all mitochondria
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The proto-mitochondrion is the hypothetical ancestral bacterial endosymbiont from which all mitochondria in eukaryotes are thought to descend, after an episode of symbiogenesis which created the aerobic eukaryotes.
Phylogeny.
The phylogenetic analyses of the few genes that are still encoded in the genomes of modern mitochondria suggest an alphaproteobacterial origin for this endosymbiont, in an ancient episode of symbiogenesis early in the history of the eukaryotes.
Although the order "Rickettsiales" has been proposed as the alphaproteobacterial sister-group of mitochondria, no definitive evidence pinpoints the alphaproteobacterial group from which the proto-mitochondrion emerged, and some contradictory evidence, especially in the early, sparse genome samplings. Martijn "et al" found mitochondria are a possible sister-group to all other alphaproteobacteria. The phylogenetic tree of the Rickettsidae has been inferred by Ferla "et al." from the comparison of 16S + 23S ribosomal RNA sequences. Geiger "et alii" (2023) propose placing the recently-discovered (2016) genus "Iodidimonas", found in a sister clade to "Rickettsidae", the "Caulobacteridae", as the closest free-living relative of mitochondria, as it possesses more metabolic products matching that of mitochondria today, such as cardiolipins and sphingolipids, and important genetic markers such as the COX operon and a counterpart to mitochondrial complex III, the bc1 complex.
Metabolism.
 reconstructed the proteome (the entire set of proteins expressed by a genome) and corresponding metabolism of the proto-mitochondrion by comparing extant alpha-proteobacterial and eukaryotic genomes. They concluded that this organism was an aerobic alpha-proteobacterium respiring lipids, glycerol and other compounds provided by the host. At least 630 gene families derived from this organism can still be found in the 9 eukaryotic genomes analyzed in the study.
See also.
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References.
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