SRA

DNA molecules are continuously released through decomposition of organic matter and are ubiquitous in most environments. Such DNA becomes fragmented and damaged (often <100bp) and may persist in the environment for more than half a million years. Fragmented DNA is recognized as nutrient source for microbes, but not as a potential substrate for bacterial evolution. Here we show that fragmented DNA molecules (longer than 20bp) that additionally may contain abasic sites, crosslinks or miscoding lesions are acquired by the environmental bacterium Acinetobacter baylyi through natural transformation. With uptake of DNA from a 43,000-yaer-old woolly mammoth bone, we further demonstrate that such natural transformation events include ancient DNA molecules. We find that the DNA recombination is RecA recombinase-independent and is directly linked to DNA replication. We show that the adjacent nucleotide variations generated by uptake short DNA fragments escape mismatch repair. Moreover double nucleotide polymorphisms appear more common among genomes of transformable than non-transformable bacteria. Our findings reveal that short and damaged, including truly ancient, DNA molecules, which are present in large quantities in the environment can be acquired by bacteria through natural transformation. Our findings open for the possibility that natural genetic exchange can occur with DNA up to several hundreds of thousands years old.