Us humans are so generous with our genes, but how exactly?

There's been a lot of chatter in the blogo/twittershere this morning about contamination of genomes, which is something I'm rather interested in, simply because I use genomes from all sorts of organisms all the time and I've come across likely contaminants several times.

The sudden interest is down to two papers about human sequences in other genomes: "Abundant Human DNA Contamination Identified in Non-Primate Genome Databases" by Longo et al. in PLoS ONE and "Opportunity and Means: Horizontal Gene Transfer from the Human Host to a Bacterial Pathogen" by Anderson and Seifert in MBio.

Longo et al. found primate-specific repetitive elements in the genomes of many different non-primates, which they put down to contamination from us DNA-shedding humans during sequencing. Anderson and Seifert on the other hand found another element in human pathogen Neisseria gonorrhoeae, which they instead put down to horizontal gene transfer.

Can they both be right? On his blog, Mark Pallen suggests the Anderson and Seifert results might also be contamination, but the debate is ongoing, so check his blog post for the full story.