WE USED to think our relationship with bacteria was simple: there were good ones that kept our digestive tracts healthy and there were bad ones that made us sick.

In recent years, this distinction has blurred. We know that many bacteria can play both roles, living happily in us or on us as part of a healthy microbiome, but capable of turning nasty under certain conditions.

Now there are claims that a truly villainous bacterium – Mycobacterium tuberculosis, which causes TB – is actually symbiotic and helped us evolve our large brains (see “Meaty puzzle: Did TB evolve to boost hungry brains?“). This is just a hypothesis, but it is clear there is still a lot to learn about the interactions between us and our microbes.

The effect of microbiomes on health is already one of the fastest moving areas of biomedicine. As resistance to antibiotics drives us to re-evaluate them, a similar look at diseases like TB could uncover life-saving knowledge.


Clarification, 25 June 2014: The third paragraph has been edited for clarity.

This article appeared in print under the headline “Me and my microbiome”