What are we?

I’m just coming from a talk by Didier Raoult, who has come to the PRBB to give a seminar (this is part of the CRG-PRBB seminars, which happen about twice a week. They are open to everyone and usually bring very good quality speakers from outside the park, many from abroad).

He told us about what he has learned by studying Ricketsia genomics (Ricketsia is a family of intracellular bacteria that cause many diseases and are usually spread by arthropods). He said many interesting things, such as the idea that the most virulent species are not so because they have a ‘virulent factor’, but rather because they have lost some regulatory genes and are not able to communicate with their host and adapt to it. For example by not dividing when there’s no food, so instead they keep on growing and eventually kill the host.

But one amazing thing I learned, and I had never realised, is that we cannot call ourselves eukaryotes, as most of us would happily do. We are, actually, an ecosystem. For every eukaryotic cell in our body, we have at least 10 archaeal cells, and who knows how many bacterial cells. So we are actually closer to be a bacterium than an eukaryote! It’s a funny thought. He went further saying that even if we got rid of all our bacteria, archaea and virus, we would still not be a pure eukaryote, since the mitochondria in each of our cells are of bacterial origin. And removing the bacteria would also not do the trick – some genes involved in mitochondrial function are nowadays integrated in the human genome.