We are all holobionts

By now, you’ve probably heard that animals in general, and humans in particular, are not alone in their bodies. In fact, we are the hosts of an extraordinary ecosystem composed of a community of bacteria, archaea, yeasts, other eukaryotes and viruses… All together, these are what we call microbiota. Lynn Margulis, went further and -in 1991- gave the name holobiont to this “supra-organism” formed by the host and its microbiota. It is good to remember that these microorganisms are not parasites, but rather organisms that live in close cooperation. Their function is so important that it has even been called the “forgotten organ”.

Within our microbiota, perhaps the best known is the intestinal microbiota (mainly in the colon), but in reality these microorganisms are found everywhere: we also have the microbiota in our mouth, skin, vagina, etc. Even mother’s milk, which we thought was sterile for a long time, today is known to have its own flora.

To give us a better idea of its size, I leave you with some numbers: Considering a human reference, defined as a man of 20-30 years, 70 kg and 170 cm (obviously, it was not me who defined it that way!) it is estimated that there are about 3.0×1013 (30,000,000,000,000) own cells and 3.8 x1013 (38,000,000,000,000) prokaryotic cells. The latter – and despite their abundance, would represent only 0.3% (0.2 kg) of the total weight. However, their gene pool is enormous, with 3.3 million genes, surpassing human genes by about 150 times! (we have about 19,000 genes). Regardless these numbers, prokaryotes are far from being the most abundant in our microbiota… both our cells and all the cells of the microbiota are susceptible to infection by a large number of specialized predators: viruses, which – despite everything – also offer us a great service.


doi: 10.1371/journal.pbio.100253

doi: 10.15698/mic2019.09.689