New study upends current theories of how mitochondria began

Parasitic bacteria were the first cousins of the mitochondria that power cells in animals and plants – and first acted as energy parasites in those cells before becoming beneficial, according to a new University of Virginia study that used next-generation DNA sequencing technologies to decode the genomes of 18 bacteria that are close relatives of mitochondria.

The study appears this week in the online journal PLOS One, published by the Public Library of Science. It provides an alternative theory to two current theories of how simple bacterial were swallowed up by host cells and ultimately became , the "powerhouse" organelles within virtually all – animal and plant cells that contain a nucleus and other features. Mitochondria power the cells by providing them with adenosine triphosphate, or ATP, considered by biologists to be the energy currency of life.

The origin of mitochondria began about 2 billion years ago and is one of the seminal events in the evolutionary history of life. However, little is known about the circumstances surrounding its origin, and that question is considered an enigma in modern biology.

"We believe this study has the potential to change the way we think about the event that led to mitochondria," said U.Va. biologist Martin Wu, the study's lead author. "We are saying that the current theories – all claiming that the relationship between the bacteria and the host cell at the very beginning of the symbiosis was mutually beneficial – are likely wrong.

"Instead, we believe the relationship likely was antagonistic – that the bacteria were parasitic and only later became beneficial to the by switching the direction of the ATP transport."

The finding, Wu said, is a new insight into an event in the early history of life on Earth that ultimately led to the diverse eukaryotic life we see today. Without mitochondria to provide energy to the rest of a cell, there could not have evolved such amazing biodiversity, he said.

"We reconstructed the gene content of mitochondrial ancestors, by sequencing DNAs of its close relatives, and we predict it to be a parasite that actually stole energy in the form of ATP from its host – completely opposite to the current role of mitochondria," Wu said.

In his study, Wu also identified many human genes that are derived from mitochondria – identification of which has the potential to help understand the genetic basis of human mitochondrial dysfunction that may contribute to several diseases, including Alzheimer's disease, Parkinson's disease and diabetes, as well as aging-related diseases.

In addition to the basic essential role of mitochondria in the functioning of cells, the DNA of mitochondria is used by scientists for DNA forensics, genealogy and tracing human evolutionary history.


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Journal information: PLoS ONE

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Oct 17, 2014
They have a done a very thorough phylogenetic study, with a better constraint than previous ones. (E.g. studies the split between pre-mitochondrion and other bacteria rather than reconstructing the proto-mitochondrion.)

That branch of rickettsiales are more often parasitic (e.g. Wolbachia), I think. The parasite start of the later mutualism is a) more ubiquitous and b) easier. It makes the endosymbiosis much more likely.

Oct 17, 2014
I would like to point out that otherwise similar pieces of code (DNA) have drastically different functions based on modifications to their processes made by other, surrounding code.

"Let's eat grandma!"
vs
"Let's eat, grandma!"

Tiny change, big difference.

This demonstrates that component similarity need not imply a functional common history.

I still see no good reason why mitochondria can't have developed from the inside out.

Maybe it developed from pieces of the chromosomal DNA which broke away from those chromosomes and was captured inside a broken piece of lipid membrane during mitosis. viola.

I also see no reason why Viruses can't be viewed as defective organelles, which may have formed in a similar manner to what I describe above, except by proteins.

Remember, not all construction is bottom up. Some is "top down".

Maybe Viral DNA is actually defective cellular DNA, rather than saying, "Some cellular DNA is Viral DNA".


Oct 17, 2014
If Mitochondria were originally parasitic, then it would make little sense for that strain of the Eukaryote to out-compete it's cousins.

Why is it so hard to believe that Nuclear DNA may have created the mitochondria as a specialized sub-cell, and then the Nuclear DNA which was redundant either disappeared or changed roles?

That seems a much easier and simpler explanation than this "cell engulfs a parasitic organism which then totally reverses itself to no longer be parasitic, all fast enough so that it out-competed it's cousins instead of just killing itself."


Oct 17, 2014
@Returners: Even before gene sequencing, the endosymbiosis process were successfully tested. "The endosymbiotic theory was advanced and substantiated with microbiological evidence by Lynn Margulis in a 1967 paper." [ http://medicalxpr....html#ms ]

This paper does yet another successful test, only with less uncertainty. And the new evidence points to a likelier process, by the way.

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