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Bacteria are known to take in long fragments of DNA, discarded by the dead cells of other organisms, and incorporate them into their own genomes. Results published today (November 18) in
Proceedings of the National Academy of Sciences show that bacteria can also integrate short and damaged stretches of DNA, even 43,000-year-old fragments extracted from a woolly mammoth bone.
Short, degraded DNA is abundant in the environment, "and if that can be used for transformation or mutagenesis, that suggests it has a much larger evolution-driving role than previously ever realized," said
Hank Seifert, a microbiologist at Northwestern University who was not involved in the study.
Natural genetic transformation, a form of
horizontal gene transfer, is the process of gobbling up chunks of other organisms' DNA present in the environment. This genetic appropriation is thought to be important in bacterial evolution and antibiotic resistance, and recent
evidence has suggested bacteria may be able to transfer DNA to human host genomes.
"It's been an assumption that short, degraded DNA is not relevant" to natural transformation, said
Søren Overballe-Petersen, a postdoctoral researcher at the University of Copenhagen and the study's lead author. But longer fragments - say, a kilobase in length - don't last very long in the environment, limiting the opportunities for bacteria to take them in. Shorter stretches of DNA, however - tens of base pairs (bp) long - can persist for hundreds of thousands of years. The researchers wanted to see whether these, too, might have some relevance in natural transformation."What are the odds of nothing happening?" asked Overballe-Petersen.
