The vital viruses that shape your microbiome and your health

Withdrawn and anxious, the mice in John Cryan’s lab were behaving like you or I might if we had experienced workplace bullying and thought we might encounter the bully again.

The good news, believe it or not, was that some of these rodents were also being fed a slurry of microbes derived from their own faeces. Unpalatable as this sounds, it had a surprisingly positive effect on their behaviour. “It was phenomenal,” says Cryan, a neurobiologist at University College Cork in Ireland. “We found that these stress-induced changes in behaviour normalised – they started to behave just like normal animals.”

Even more surprising, this mental transformation wasn’t brought about by changing the bacteria in their guts, but by tinkering with another crucial facet of the microbiome whose importance is only now being recognised: viruses.

It turns out that we are riddled with these. Not the ones that make us unwell, but trillions of stowaways that play a crucial role in cultivating a beneficial microbiome and making us healthier in turn. Recent research shows that the influence of this “virome” can be found across the body, from the blood to the brain. The hope is that by tweaking it, we could find new ways of treating various ailments, from inflammatory bowel disease and obesity to anxiety.

Microbiome diversity

The past decade has seen a surge of interest in the microbiome – all the really tiny things that live on and in us – but this has largely focused on bacteria. The assumption until recently was that…