While most of us pay little attention to the food we eat after chewing and swallowing, the next step in digestion is only the beginning of an hours-long process of extracting the nutrients we need to live.

Eating not only nourishes us, it nourishes a vast microbial community in our gut called the microbiota. Like an extension of our immune system, our microbiota helps us stay healthy in a number of ways, like blocking pathogens from making us sick.

But also like our immune system—in the context of autoimmunity, allergies or septic shock—too much of a good thing can be harmful. While the majority of our microbiota lives safely in our large intestine, some patients develop a dangerous overgrowth of bacteria in their small intestine, where most of our dietary nutrients get absorbed.

This overgrowth can lead to a number of problems including vitamin B12 deficiency, even despite the consumption of foods high in vitamin B12.

To better understand how our gut microbes affect our ability to absorb nutrients from our diet, scientists at Yale have uncovered the tools gut microbes themselves use to consume the nutrients they need.

Published today in eLife, scientists at the Yale Microbial Sciences Institute describe the molecular “forks and spoons” that allow gut microbes to scoop up and ingest nutrients like vitamin B12 as they pass through our digestive tract.

“To our great surprise, we found that many members of our microbiota decorate their cell exteriors with proteins called BtuG that grab onto vitamin B12 with extraordinary binding strength,” said Aaron Wexler, a former graduate student in the lab of the study’s senior author, Andrew Goodman, associate professor of microbial pathogenesis at Yale School of Medicine.

In fact, the scholars found that bacterial proteins bind to vitamin B12 so strongly that they can even pry it away from our own vitamin B12 binding protein.

The findings suggest that constant competition for vitamin B12 among gut microbes over vast stretches of time has selected for species with an ever-greater ability to capture this essential nutrient.

Given the many medical conditions now linked to the microbiota, building our understanding of both the benefits and detriments that our microbiota bring to us will be of increasing value as we move closer towards the goal of personalized medical care.

Contact: jon.atherton@yale.edu