Gonorrhea acquires a piece of human DNA

Feb 14, 2011

If a human cell and a bacterial cell met at a speed-dating event, they would never be expected to exchange phone numbers, much less genetic material. In more scientific terms, a direct transfer of DNA has never been recorded from humans to bacteria.

Until now. Northwestern Medicine researchers have discovered the first evidence of a human fragment in a – in this case, Neisseria gonorrhoeae, the bacterium that causes . 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.

"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, professor of microbiology and immunology at Northwestern University Feinberg School of Medicine. "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 can adapt to the host."

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 paper will be published Feb. 14 in the online journal mBio.

The finding suggests gonorrhea's ability to acquire DNA from its human host may enable it to develop new and different strains of itself. "But whether this particular event has provided an advantage for the gonorrhea bacterium, we don't know yet, " Seifert said.

Every year an estimated 700,000 people in the United States and 50 million worldwide acquire gonorrhea. While the disease is curable with antibiotics, only one drug is now recommended for treatment because the disease developed resistance to previously used antibiotic options over the past four decades.

Gonorrhea is a particularly serious disease for women. If left untreated, gonorrhea can lead to pelvic inflammatory disease, a painful condition that can cause sterility and ectopic pregnancy. In rare cases, men and women can develop a form of the disease that leaves the genital tract and enters the bloodstream, causing arthritis and endocarditis, an infection of the inner lining of the
heart.

An ancient disease that sounds like gonorrhea is described in the Bible, noted Seifert, who has studied the disease for 28 years. Most of his research focuses on how the bacterium evades the human immune system by altering its appearance and modulating the action of white blood cells.

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.

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

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

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kevinrtrs
1 / 5 (10) Feb 14, 2011
An interesting question to answer would be : Why is Gonorrhea exclusive to humans?
If it is exclusive how did it "evolve" such that it finally stopped using other hosts and focused solely on humans instead? What other hosts could it have used? What is it's makeup that it needs[?] to be active on humans, i.e. why not on monkeys or chimps?

If it turns out that Gonorrhea never had any other hosts what would that imply regarding human beings? What would it imply regarding Gonorrhea?

The possibility therefore exists that it was specifically made to plague human beings, however remote one would like that possibility to be. Before jumping down my throat on such a suggestion, perhaps a little research about Gonorrhea is required?

Grallen
5 / 5 (6) Feb 14, 2011
The possibility therefore exists that it was specifically made to plague human beings

It means we are numerous and wide spread. A stable breeding ground for the bacterium. It probably evolved from one of the others mentioned:
Anderson also screened the bacterium that causes meningitis, Neisseria meningitidis, and is very closely related to gonorrhea bacteria at the genetic level.
gvgoebel
5 / 5 (3) Feb 14, 2011
There is nothing unusual about species-specific pathogens and parasites. Just as certainly as two different organisms can acquire a tight symbiotic relationship, they can acquire a tight antagonistic relationship.

One of the reasons that we were able to exterminate smallpox was because it had no animal hosts. There are a number of other afflictions that are similarly vulnerable.
Ramael
not rated yet Feb 15, 2011
Probably became exclusive when it took on human dna.
jmcanoy1860
not rated yet Feb 15, 2011
The fact that it is sexually transmitted and that humans like to boink AND have a large population should give you a hint kevin.

Either evolution or some deity decided to "specially design" diseases against humans? I'll stick with science, thanks.
gvgoebel
5 / 5 (1) Feb 15, 2011
I might add on species-specificity: ever met any humans who came down with a case of feline leukemia virus or canine distemper?

The pattern of cross-species disease transmission is very confusing and I would imagine it would take a research degree to sort it out at all. Parrot fever (psittacosis) and rabbit fever (tularemia) are dangerous enough to humans that they were both researched as biowarfare agents.

If such patterns supposedly reflect Design, personally I think it suggests one Designer working for us, the Other working against us. I've long wondered why "Manichean dualism" never really caught on -- it seems a better model of reality than the alternative.

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