Bacteria make up a considerable part of our body and help us with some bodily functions—but a little bit of motivation is necessary to keep these tiny organisms in check.

A recent Duke study has shown that hosts manipulate the nutrients that bacteria are able to receive. They found that microbes within human bodies actually have access to less nitrogen—a key bacterial nutrient—compared to free-living bacteria.

Aspen Reese, a former Ph.D. candidate at Duke and current microbial ecologist junior fellow at Harvard Society of Fellows, was the lead author in the paper that investigated why these microbes serve us and how our actions could change that. Reese said her research highlighted the importance of nitrogen, which has previously received little attention, in the gut’s microbiome.

"There are likely still many opportunities to discover new nitrogen-based interventions for manipulating the microbiota to improve health,” Reese said. “In my own work, I am focusing on studying how natural variation in nitrogen availability is jointly managed by the host and microbiota. Others will likely focus on new dietary manipulations or prebiotics that alter nitrogen availability to shape the microbiota.”

Lawrence David, assistant professor of molecular genetics and microbiology at the Duke University School of Medicine and senior author of the paper, served as mentor in carrying out the research that Reese was doing in his lab. David explained that the study revealed an important dynamic of the host-bacteria dynamic.

“This teaches us a bit more about why bacteria in the gut are nice to people—why they cooperate with us, the host,” he said.

Reese found that bacteria cooperate because they depend on humans to provide nutrients that they might not otherwise get. This then led to the conclusion that, if bacteria depend on us for nutrients, then those nutrients must be scarce. However, the availability depends on the human’s diet.

“We were looking at nitrogen, which shows up in protein,” David said. “So the benefit to us, the host, goes away if too much nitrogen is consumed, like if someone is eating a lot of meat. That’s why diets rich in meat might not be beneficial from a microbiome standpoint.”

While the microbes are starving for nutrients, they will help the host in digestion, immunity, mental health and more, he added. But the relationship is not balanced, and it would seem that if the microbes get the nutrients they need, they will stop assisting the human.

Although they did not measure the specific outcomes for the host, the team at Duke is moving away from analyzing microbiota and their nitrogen consumption. Instead, David mentioned that the next step in this research will be to look at the exact relationship between people’s diet and their microbiome.

This will initially focus on over-the-counter supplements, such as vitamins.

“Millions of Americans take these, and they might have implications to the microbiome,” David said. “This includes working with the Duke Cancer Institute to examine how certain kinds of nutrient sources can protect against diseases. This could apply to general everyday health or more serious chronic issues.”