A chimeric prokaryotic ancestry of mitochondria and primitive eukaryotes

We provide data and analysis to support the hypothesis that the ancestor of animal mitochondria (Mt) and many primitive amitochondrial (a-Mt) eukaryot es was a fusion microbe composed of a Clostridium-like eubacterium and a Su lfolobus-like archaebacterium. The analysis is based on several observation s: (i) The genome signatures (dinucleotide relative abundance values) of Cl ostridium and Sulfolobus are compatible (sufficiently similar) and each has significantly more similarity in genome signatures with animal Mt sequence s than do all other available prokaryotes. That stable fusions may require compatibility in genome signatures is suggested by the compatibility of pla smids and hosts. (ii) The expanded energy metabolism of the fusion organism was strongly selective for cementing such a fusion. (iii) The molecular ap paratus of endospore formation in Clostridium serves as raw material for th e development of the nucleus and cytoplasm of the eukaryotic cell.