Alexander Hartley asked:
Does the DNA of food survive the human digestive system?
Alexander Hartley, Norwich, Connecticut, USA
Chris - This is very interesting because originally, people thought the answer to this was no. But then, about 4 years ago, there was a lovely paper published in the journal Nature where scientists had been taking samples of seawater. They had studied the DNA of these seawater samples and they had found this combination of genes which broke down a certain set of sugars in what we know is seaweed. They thought this was brand new – no one had discovered this before. So, they had a look in this database of genes which is all over the world. And they were rather annoyed to see that someone had published a very similar DNA sequence previously and they thought, “Who’s done that> that's annoying.” But they found that these were all from Japan and they all corresponded to samples taken from the intestines of people in Japan. They realised what's happened is that people eating sushi in Japan - because that's got seaweed in it - and the bacteria they were studying in the sea were eating seaweed, the people had eaten some seaweed and the DNA from the microbes in the seaweed had leached out into their intestines and those people’s own intestinal bacteria had picked up the DNA, and incorporated the genes into it, which is, as one person put it, rather like, you going into a restaurant and someone equipping you with a brand new knife and fork to eat a rather tough steak with because you see a knife and fork, “I think I’ll have that one instead of the blunt knife I've got already.” So, yes, DNA can survive transit through the human digestive tract and other organisms can actually incorporate it which I think that's absolutely stunning.
Richard - It’s amazing, isn’t it? I'm stunned that you look at the process of something passing through us and everything is sort of subjected to the acid and the attack by the body, and all the bacteria, and yet, DNA can survive that. That is incredible.