Before the age of better food hygiene, our meals used to provide a rich source of foreign bacteria that our microbiome could plunder for genetic tools. Bacteria trade genes as easily as humans trade gifts. For example, the gut bacteria of Japanese people have borrowed genes from a marine species, which now allows them to digest the special carbohydrates in seaweed. The marine bacterium eats seaweed, including the types that are used to make nori, a common sushi ingredient. In the past, when diners wolfed down morsels of nori, some also swallowed seaweed-eating bacteria, which traded genes with those in their own guts.
This wouldn’t happen nowadays because nori is roasted before being eaten. In fact, processing food presents a blockade to bacteria from the outside world and as a result, Western gut communities have become gentrified. They lack genetic diversity, and they have few ways of increasing it.
Images by Alice Wiegand, Alex Kovach, Tristan Barbeyron and Mirjam Czjzek