The Origin of Mitochondria and Endosymbiosis
Overwhelming evidence supports the endosymbiosis theory that mitochondria originated once from within a specific group of bacteria called α-proteobacteria. However, significant questions remain. Early studies based on a few genes placed the mitochondrial ancestor near the Rickettsia species , but this has been challenged by us and by other groups based on recent, genome-level phylogenetic analyses [3,20]. Placing this ancestral bacterium correctly within the bacterial phylogenetic tree is of great importance for elucidating the origin and early evolution of mitochondria and eukaryotes. It would shed light on many fascinating questions: Was the mitochondrial ancestor free-living or an obligate intracellular symbiont? What was its genetic make-up? Was its genome complex or already streamlined? We'll continue work on this exciting question using a comparative genomics approach. In the long run, we hope this research would lead us toward a better understanding of the bacterial endosymbiosis in general.