Proto-mitochondrion

The proto-mitochondrion is the hypothetical ancestral bacterial endosymbiont from which all mitochondria in eukaryotes are thought to descend.

Proto-mitochondrion
Scientific classification
Domain:
Bacteria
Phylum:
Proteobacteria
Class:
Alphaproteobacteria
Order:
Rickettsiales (?)

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. Although the order Rickettsiales has been proposed as the alpha-proteobacterial sister-group of mitochondria, there is no definitive evidence as to from which alpha-proteobacterial group the proto-mitochondrion emerged. Martijn et al. found mitochondria are a possible sister-group to all other alphaproteobacteria.[1]

Schematic ribosomal RNA phylogeny of Alphaproteobacteria
  Magnetococcidae  

  Magnetococcus marinus

 
 
  Caulobacteridae  
 

  Rhodospirillales, Sphingomonadales,
  Rhodobacteraceae, Rhizobiales, etc.

 
 

  Holosporales

 
 
  Rickettsidae  
  Pelagibacterales  
  Pelagibacteraceae  
 

  Pelagibacter

 
 
 

  Subgroups Ib, II, IIIa, IIIb, IV and V

 
 
  Rickettsiales  
 

  Proto-mitochondria

 
 
  Anaplasmataceae  
 
 
 

  Ehrlichia

 
 

  Anaplasma

 
 
 

  Wolbachia

 
 
 

  Neorickettsia

 
 
 
  Midichloriaceae  
 

  Midichloria

 
 
  Rickettsiaceae  
 

  Rickettsia

 
 

  Orientia

 
 
 
 
 
 
 
The cladogram of Rickettsidae has been inferred by Ferla et al. [2] from the comparison of 16S + 23S ribosomal RNA sequences.

Metabolism

Toni Gabaldón and Martijn Huynen (2003) 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 catabolyzing 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.[3]

See also

References
  1. Martijn, Joran; Vosseberg, Julian; Guy, Lionel; Offre, Pierre; Ettema, Thijs J. G. (2018). "Deep mitochondrial origin outside the sampled alphaproteobacteria". Nature. 557 (7703): 101–105. Bibcode:2018Natur.557..101M. doi:10.1038/s41586-018-0059-5. ISSN 0028-0836. PMID 29695865.
  2. Ferla MP, Thrash JC, Giovannoni SJ, Patrick WM (2013). "New rRNA gene-based phylogenies of the Alphaproteobacteria provide perspective on major groups, mitochondrial ancestry and phylogenetic instability". PLOS One. 8 (12): e83383. doi:10.1371/journal.pone.0083383. PMC 3859672. PMID 24349502.
  3. Gabaldón, T.; et al. (2003). "The proto-mitochondrial metabolism". Science. 301 (5633): 690. doi:10.1126/science.1085463. PMID 12893934.
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