Despite its diversity, the skin microbiome is a tiny country village compared to the bustling metropolis inside your bowels. The dark corridors of your intestine house more bacteria than any other part of your body. A team of international scientists led by Junjie Qin and Ruiqiang Li discovered that each of our bowels carries at least 160 bacterial species. Together, our collective guts have just under 3.3 million bacterial genes, more than 150 times as many as reside in our own genomes. They also showed that the gut microbiome of a healthy person looks very different to that of someone with a bowel condition like Crohn’s disease or ulcerative colitis.

Despite this diversity, Peer Bork has shown that the gut bacteria of people from Europe, North American and Japan collapse into three enterotypes, or gut types. These clusters cut across age, gender, body weight and nationality. Each produces energy in a slightly different way, manufactures a different vitamin and may affect our susceptibility to different diseases.

The quest to understand gut microbes may seem like an arcane niche of science, but it’s actually very important for public health. We rely on these microscopic passengers more than we realise. They harvest energy from our food, provide us with nutrients that would otherwise be denied to us, prevent the growth of harmful bacteria, and more. In many ways, they’re like a forgotten organ. They can also go rogue, changing their community in ways that are linked to obesity or bowel diseases.

Image by Med. Mic. Sciences Cardiff Uni, Wellcome Images