From a bacteria’s perspective, the environment is one big DNA waste yard. Now researchers from Denmark and Norway have shown that bacteria can take up small as well as large pieces of old DNA from this scrapheap and include it in their own genome.
This discovery may have major consequences both in connection with resistance to antibiotics in hospitals and in our perception of the evolution of life itself. Our surroundings contain large amounts of strongly fragmented and damaged DNA, which is being degraded. Some of it may be thousands of years old.
Laboratory experiments with microbes and various kinds of DNA have shown that bacteria take up very short and damaged DNA from the environment and passively integrate it in their own genome.
Furthermore, this mechanism has also been shown to work with a modern bacteria’s uptake of 43.000 years old mammoth DNA.
The discovery of this second-hand use of old or fragmented DNA may have major future consequences. Postdoc Søren Overballe-Petersen from the Center for GeoGenetics at the Natural History Museum of Denmark first author on the paper, says it is well-known that bacteria can take up long intact pieces of DNA. “But so far the assumption has been that short DNA fragments were biologically inactive. Now we have shown that this assumption was wrong. As long as you have just a tiny amount of DNA left over there is a possibility that bacteria can re-use the DNA.”
“One consequence of this is in hospitals that have persistent problems with antibiotic resistance,” says Kaare M. Nielsenfrom University of Tromsø in Norway. “In some cases, they will have to start considering how to eliminate DNA remnants. So far, focus has been on killing living pathogen bacteria, but this is no longer enough in the cases where other bacteria afterwards can use the DNA fragments which contain the antibiotic resistance.
“The research group’s results reveal that the large reservoir of fragments and damaged DNA in the surroundings preserve the potential to change the bacteria’s genomes even after thousands of years. This is the first time a process has been described which allows cells to acquire genetic sequences from a long gone past. We call this phenomenon “Anachronistic Evolution” or “Second-hand Evolution.”