Evolution of bacterial endoparasites as a model for the origin of mitochondria

Through its nearly 4 billion year history, life has undergone a number of major evolutionary transitions. One involved the acquisition of mitochondria by the ancestor of nucleated cells. The acquisition of mitochondria enabled these cells to respire oxygen, greatly increasing the energy they could obtain from resources like simple sugars and amino acids. Though it is widely accepted that mitochondria originated as free-living bacteria, little is known about how they came to be symbionts of their hosts. The aim of my research is to develop a model using extant microbial species that recapitulates the initial stages of this major evolutionary transition. To that end I will apply selection on the parasitic bacterium Bdellevibrio bacteriovorus and its host/prey Escherichia coli that encourages the former to reside in the latter for progressively longer periods of time without killing it. My ultimate goal is to evolve a Bdellevibrio bacterium that can reside indefinitely inside its host, which would serve as a model for the origin of another endosymbiont, the mitochondrion. No experimental model currently exists for the origin of mitochondria. By investigating the genetic basis of the transition from a parasitic to a commensal relationship between these bacteria I hope to gain insight into one of the key innovations that led to emergence of complex life that includes fungi, plants and animals, including humans