Those with even the most limited knowledge of cellular biology will recognize these jellybean-shaped organelles known as "mitochondria". They're the power houses for all eukaryotic cells, providing a means for energy creation and survival, and they're perhaps one of the most peculiar organelles in ours and every organism's bodies. Through the use of simple components, sugar, oxygen and transfer molecules, the mitochondria are able to create and store energy through the simple movement of electrons from one bond to another. And in spite of conflicting theories describing their possible origins, a new study at the University of Virginia is proving that the energy creators weren't always self-sustaining components.
Published this week in the journal PLOS One, researchers at the University of Virginia have discovered that the energy powerhouses may have once been energy parasites, like their bacteria relatives, once draining the energy instead of creating it. Using next-generation DNA sequencing technologies, and an understanding of applied genomics specific to the genetic information found in mitochondria (which differs from that of your typical DNA), the researchers were able to decode the genomes of 18 bacteria species, which they believe to be the closest relatives to the mitochondria.
"We believe this study has the potential to change the way we think about the event that led to mitochondria" lead author of the study, Martin Wu says. "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."
Contemporary biology posits two refined theories that have developed over the centuries. Believed that mitochondria were originally ancient bacteria, the two theories posit that host cells engulfed the bacteria and in the process created mitochondria. But, based on the assumption that the bacteria was always a beneficial energy-producing part of the symbiosis seen in current eukaryotic cells, the study proposes that these theories could both be false. Creating an alternative theory that contradicts all current models, researchers now believe that early mitochondria could have sucked pre-historic cells dry of energy, before deciding to help out.
"Instead, we believe the relationship likely was antagonistic" Wu says. "[We believe] that the bacteria were parasitic and only later became beneficial to the host cell by switching the direction of the ATP transport."
The discovery came from wide analyses of multiple bacterial genomes, and by using current DNA models for mitochondrion as well as models that show similar mutations called "Single Nucleotide Polymorphisms" (SNPs for short) that have arisen over millennia of evolution, researchers were able to track down some of the closest living relatives that they think mitochondria may have derived from.
"We reconstructed the gene content of mitochondrial ancestors, by sequencing DNAs of its close relatives" Wu says. "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."