There鈥檚 nothing like a personalised gift to make your lover feel extra special this Valentine鈥檚 day, but perhaps not this one: a little piece of human DNA wrapped in the genome of gonorrhoea bacteria.
and Mark Anderson at Northwestern University in Chicago analysed the genome sequences of 14 samples of 鈥� the bacteria that causes the sexually transmitted disease. When the pair ran the sequences through a computer to look for contamination, they found a human fragment of DNA present in three of the isolates.
鈥淲e have never seen a direct DNA jump from a mammalian genome to a bacterial genome,鈥� says Seifert, who was surprised by the discovery. The jump must have happened via a process known as horizontal gene transfer.
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The pair looked for the same human DNA fragment in the genetically related bacterium Neisseria menigitidis, known to cause meningitis. 鈥淲e screened many isolates and it wasn鈥檛 present,鈥� says Seifert. That means the transfer to 狈.听驳辞苍辞谤谤丑辞别补别 must have occurred since the two bacterial species diverged around 200,000 years ago.
Mimic the host
鈥淭he bacterium is getting a genetic sequence from the very host it鈥檚 infecting,鈥� Seifert says. 鈥淭hat could have far-reaching implications as far as how the bacteria can adapt to the host.鈥�
, a microbiologist at the University of Oxford, agrees. 鈥淚f [the human DNA] enables the bacteria to mimic the host or interact with the host, it would be a big deal.鈥�
But exactly what role 鈥� if any 鈥� the human DNA performs in the bacteria is a mystery. 鈥淭he unsettling part of the story is that we know of no reason for it to be there,鈥� Seifert says.
What鈥檚 it doing in there?
In humans, the sequence 鈥� known as L1 鈥� can move around the genome. The fragment in the bacteria, however, lacks key parts of its sequence, so remains static. The sequence doesn鈥檛 seem to have any effect on its new genetic neighbours, and isn鈥檛 producing a functional protein, either, adds Seifert.
It鈥檚 possible that the DNA is doing nothing at all. The gene transfer is likely to have been a random event, and the human DNA could be kept on by the bacteria merely because it鈥檚 not incurring any kind of cost.
鈥淚t鈥檚 a bit of a frustrating story,鈥� Seifert says. 鈥淲e鈥檙e looking for functions but we鈥檙e not optimistic.鈥�
Journal reference: , DOI: 10.1128/mbio.00005-11
