Human DNA discovered in gonorrhea

Scientists have found their first evidence of gene transfer from humans to bacteria  – and, guess what, it’s gonorrhea that’s the lucky recipient.

Gonorrhea, transmitted through sexual contact, is one of the oldest recorded diseases and one of a few exclusive to humans. Something that sounds very much like it is described in the Bible.

Now, Northwestern Medicine researchers have discovered a human DNA fragment in Neisseria gonorrhoeae, and say the gene transfer appears to be relatively recent.

“This has evolutionary significance because it shows you can take broad evolutionary steps when you’re able to acquire these pieces of DNA,” said study senior author Hank Seifert.

“The bacterium is getting a genetic sequence from the very host it’s infecting. That could have far-reaching implications as far as how the bacteria can adapt to the host.”

It’s known that gene transfer occurs between different bacteria and even between bacteria and yeast cells – but never between two species so very different.

“Whether this particular event has provided an advantage for the gonorrhea bacterium, we don’t know yet,” Seifert said.

The gene transfer was discovered when the genomic sequences of several gonorrhea clinical isolates were determined at the Broad Institute in Cambridge, Massachussetts. 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.

The team sequenced the fragment to confirm it was indeed identical to the human one, and also found that the human sequence was present in about 11 percent of the screened gonorrhea isolates.

The team also screened the bacterium that causes meningitis, Neisseria meningitidis – very closely related to gonorrhea bacteria at the genetic level. There was no sign of the human fragment, suggesting the gene transfer is a recent evolutionary event.

“The next step is to figure out what this piece of DNA is doing,” Seifert said.