Werren doesnt believe that the Wolbachia intentionally insert their genes into the hosts. Rather, it is a consequence of cells routinely repairing their damaged DNA. As cells go about their regular business, they can accidentally absorb bits of DNA into their nuclei, often sewing those foreign genes into their own DNA. But integrating an entire genome was definitely an unexpected find.
Werren and Clark are now looking further into the huge insert found in the fruitfly, and whether it is providing a benefit. The chance that a chunk of DNA of this magnitude is totally neutral, I think, is pretty small, so the implication is that it has imparted of some selective advantage to the host, says Werren. The question is, are these foreign genes providing new functions for the host" This is something we need to figure out.
Evolutionary biologists will certainly take note of this discovery, but scientists conducting genome-sequencing projects around the world also may have to readjust their thinking.
Before this study, geneticists knew of examples where genes from a parasite had crossed into the host, but such an event was considered a rare anomaly except in very simple organisms. Bacterial DNA is very conspicuous in its structure, so if scientists sequencing a nematode genome, for example, come across bacterial DNA, they would likely discard it, reasonably assuming that it was merely contaminationperhaps a bit of bacteria in the gut of the animal, or on its skin.
But those genes may not be contamination. They may very well be in the hosts own genome. This is exactly what happened with the original sequencing of the genome of the anannassae fruitflythe huge Wolbachia insert was discarded from the final assembly, despite the fact that it is part of the flys genome.
In the early days
|Contact: Jonathan Sherwood|
University of Rochester