Some years ago, when Jennifer Pluznick was nearing the end of her training in physiology and sensory systems, she was startled to discover something in the kidneys that seemed weirdly out of place. It was a smell receptor, a protein that would have looked more at home in the nose. Given that the kidneys filter waste into urine and maintain the right salt content in the blood, it was hard to see how a smell receptor could be useful there. Yet as she delved deeper into what the smell receptor was doing, Pluznick came to a surprising conclusion: The kidney receives messages from the gut microbiome, the symbiotic bacteria that live in the intestines.

In the past few years, Pluznick, who is now an associate professor of physiology at Johns Hopkins University, and a small band of like-minded researchers have put together a picture of what the denizens of the gut are telling the kidney. They have found that these communiqués affect blood pressure, such that if the microbes are destroyed, the host suffers. The researchers have uncovered a direct, molecular-level explanation of how the microbiome conspires with the kidneys and the blood vessels to manipulate the flow of blood.