There’s a lot of degraded DNA in the environment. It’s estimated that more than 1,000 tons of sedimentary DNA is released by rivers every year. The detritus is from plants and animals that have reached the end of life by natural and not so natural means. With soil constantly being exposed through erosion, glacial retreat, and overflowing rivers, some of this DNA could be several centuries old.
With that amount of degraded DNA lying around, is it possible that bacteria could absorb some of it into their genomes? Led by Søren Overballe-Petersen, Ph.D., researchers at the University of Copenhagen decided to find out.
Most of the free DNA in the environment is < 100 bp. The team set out to find the lower limit of bacterial transformation, identifying a process that isn’t dependent on the presence of RecA, the protein that integrates DNA into the genome. This basal transformation occurred with fragments down to 20 bp. It even occurred with short modern DNA that had been damaged with uracils, crosslinks, base-loss, nicks, gaps, and tails in the DNA substrate.
More surprising, basal transformation occurred with 43,000-year–old woolly mammoth DNA. The ancient DNA didn’t transform the bacteria into a new organism, as it did in the movie Jurassic Park. However, the mammoth DNA was as easily integrated into the bacterial genome as modern DNA.
The team succeeded in disputing the theory that only long fragments (> 300 bp) of DNA can be absorbed through horizontal gene transfer. They also raised the possibility that basal transformation was present in early primitive cells and impacts bacterial evolution. It could also be partially responsible for the increase of antibiotic-resistant strains of pathogens in hospital settings.
Image: Spaully, Wikimedia commons