Are we more bacteria than human ?

Didn’t you have this discussion with your scientific minded friends: so many bacteria in your intestine, on your skin etc. that actually you may be more bacteria than human? I sure had this discussion with two Ivy League university professors who were 100% sure there was more bacteria than human DNA in the typical 70kg man.

So what are the orders of magnitude?

A recently published PNAS article sets the records straight:

  1. There are slightly (<3%) more bacteria than human cells in a human body
  2. Their total mass is 350 times less than that of human cells

That implies that total DNA content is about 1000 times less than total human DNA as the number of cells is about the same and the human genome at ~3 billion base pair is 1000 times the typical bacterial genome size.

Of course that’s without counting mitochondria which might be considered as endosymbiotic bacteria.

So sure, bacteria in a human body are important, but not completely overwhelming our “own” genetic information :-)