Mitochondria, which power the cells of plants and animals, are believed to have acted as "energy parasites" before becoming beneficial to their hosts.
Researchers used DNA sequencing to decode the genomes of 18 bacteria that are mitochondria relatives, the University of Virginia reported. Mitochondria are believed to have hit the scene about two billion years ago, but little is known about their origins.
"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."
As an alternative to these past theories, the new study suggests early mitochondria relatives were parasitic to their hosts, and did not become beneficial until switching the direction of their ATP transport years down the road. The researchers believed once these mitochondria developed to become beneficial, it helped fuel the development of today's vast biodiversity.
"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.
The researchers were also able to pinpoint human genes that were derived from mitochondria, which could help them gain insight into the genetic basis of human mitochondrial dysfunctions contributing to several diseases. Some of these conditions include "Alzheimer's disease, Parkinson's disease and diabetes," the University of Virginia reported.
The findings appear in this week's edition of the journal PLoS ONE.
