Gene transfer from bacteria to eukaryotes

We already know that bacteria swap genes among themselves so readilty that Ford Doolittle, among others, argue that relationships among them is better described by a network than by an evolutionary tree. We also already know that many genes that were part of the original photosynthetic symbiont that evolved into the chloroplast in green plans have been transferred to the nucleus (e.g., tufA). We even already know that many groups of animals host endosymbiotic bacteria belonging to the genus Wolbachia and that these bacteria sometimes play an important role in reproductive isolation between species (e.g., in the wasp Nasonia).

In today's Science Julie C. Dunning Hotopp and her co-authors report multiple cases in which Wolbachia genes have been transferred to the nucleus of their host. In Drosophila ananassae almost the entire genome (ca. 1 mb) had been transferred, and that about 2% of the transferred genes are transcribed. In Nasonia they identified only small transfers (<500 bp).

ThIs study raises one very intriguing question: Is lateral gene transfer (relatively) common only from endosymbiotic bacteria to hosts or is it (relatively) common among all bacteria? As the authors point out, “[w]hole eukaryote genome sequencing projects routinely exclude bacterial sequences on the assumption that these represent contamination.” As a result, current whole-genome sequences can't be used to answer this question. Only the time-consuming experimental approach Hotopp and her colleagues used can determine whether the bacterial sequences detected in whole-genome projects are truly contamination, or if they represent nuclear copies of bacterially-derived DNA.