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Star Wars-Inspired Midichlorian Bacterium Offers Glimpse Into Origin Of Life

The Midichlora mitochondrii bacterium whose name was inspired by the Star Wars films has provided new clues into the evolution of our cells and how they came to possess energy-producing mitochondria.

| December 12, 2011 | In the Lab

AsianScientist (Dec. 12, 2011) – A new study, published in this month’s issue of Molecular Biology and Evolution, has revealed that mitochondria may have entered our cells through a parasitic bacterium that used a tail to swim and could survive with almost no oxygen.

This finding sheds new light on a process recognized as one of the major transitions in the history of life on Earth and challenges traditional explanations that the ancestors of mitochondria were passive bacteria engulfed by a primordial cell between one and a half and two billion years ago.

Researchers from Italy, Spain, and Australia investigated the Midichloria mitochondrii – named after the Star Wars microbes, called Midichlorians, that live symbiotically inside cells and when present in sufficient numbers, could allow their symbiont to detect the Force. In the films, midi-chlorian count was an indicator of the potential of the Force, with the highest known midi-chlorian count of over 20,000 per cell belonging to Anakin Skywalker, who later turned to the dark side as Darth Vader.

M. mitochondrii was used for the study because its genome had never been analyzed and it is the only bacterium known to be able to enter the mitochondria of living cells.

After determining the DNA sequence of its entire genome, co-author Dr. Nathan Lo from the University of Sydney’s School of Biological Sciences and collaborators found that the bacterium contained 26 genes coding for an entire flagellum – including all key components such as hook, filament and basal body.
 

(A) Midichloria mitochondrii inside the mitochondria of the tick Ixodes ricinus. (B) Structure of the M. mitochondrii genome. The fifth circle from the outside shows the position of flagellar genes.

The team also found a second set of genes, never seen before in bacterial relatives of mitochondria, which coded for enzymes which would allow the bacterium to survive in low-oxygen environments.

It has long been thought that mitochondria came to reside in our cells when an ancient eukaryotic cell, a cell that contains both a nucleus and mitochondria, engulfed the mitochondrial ancestor.

As our cells inherited two sets of genes from the common ancestor shared by M. mitochondrii and our own mitochondria, the findings indicate that it was highly likely that the mitochondrial ancestor had a flagellum, was able to move and possibly acted as a parasite, rather than prey, on early eukaryotic cells.

“Our results show the ancestor of mitochondria probably played a much more active, even parasitic, role in the early interactions with its eukaryotic host than previously thought. They also explain how the relationship could have evolved in the low-oxygen environments of two billion years ago,” said Dr. Lo.

Dr. Lo hopes that the study’s findings will cause a rethink of how the symbiosis between mitochondria and eukaryotic cells originally developed – one of the most controversial topics in biology.

The article can be found at: Sassera D et al. (2011) Phylogenomic Evidence for the Presence of a Flagellum and cbb3 Oxidase in the Free-Living Mitochondrial Ancestor.

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Source: University of Sydney.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

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