The first evidence of a human DNA fragment in a bacterial genome has been discovered by Northwestern Medicine researchers.
In this case, the transfer was observed in Neisseria gonorrhoeae, the bacterium that causes gonorrhea.
Further research showed the gene transfer appears to be a recent evolutionary event.
The discovery offers insight into evolution as well as gonorrhea's nimble ability to continually adapt and survive in its human hosts. Gonorrhea, which is transmitted through sexual contact, is one of the oldest recorded diseases and one of a few exclusive to humans.
It's known that gene transfer occurs between different bacteria and even between bacteria and yeast cells.
"But human DNA to a bacterium is a very large jump," said lead author Mark Anderson, a postdoctoral fellow in microbiology.
"This bacterium had to overcome several obstacles in order to acquire this DNA sequence."
The gene transfer was discovered when the genomic sequences of several gonorrhea clinical isolates were determined at the Broad Institute in Cambridge, Mass. Three of the 14 isolates had a piece of DNA where the sequence of DNA bases (A's, T's, C's and G's) was identical to an L1 DNA element found in humans.
In Seifert's Feinberg lab, Anderson sequenced the fragment to reconfirm it was indeed identical to the human one. He also showed that this human sequence is present in about 11 percent of the screened gonorrhea isolates.
The study has been published in the online journal mBio.