Soil microbes metabolize the same polyphenols found in chocolate, wine

Fruits, vegetables, red wine and chocolate are all rich in polyphenols, plant compounds that double as cancer-fighting antioxidants. Humans can access these foods' health benefits because the microbes in our guts happily feast on them, breaking them down into smaller chemical components.

Microbiome scientists at Colorado State University wanted to know if the microbes can also break down these same polyphenols in systems outside the human body, including in the microbial wild west of soils.

A research team led by Kelly Wrighton has uncovered new insights into the role of polyphenols in the soil microbiome, known as a black box for its complexity. The scientists offer an updated theory that soils -- much like the human gut -- can be food sources for the microbes that live there. Their results could upend a long-held theory that, under certain conditions, soil microbes cannot access polyphenols and could thus be used as carbon traps to reduce greenhouse gases in the atmosphere.

"Our study opens the door for further study of polyphenol metabolism in the field and how it fits into natural carbon cycles," said soil and crop science researcher Bridget McGivern, first author on a paper published in Nature Communications.

The U.S. National Science Foundation-funded research involved precisely monitored soil samples subjected to high-resolution analytical chemistry in the lab. The researchers set out to prove the concept that microbes in soil, under oxygen-free conditions, do in fact break down polyphenols, likely releasing carbon dioxide.

These experiments fly in the face of the longstanding "enzyme latch" theory that soil microbes do not metabolize polyphenols when oxygen is not freely available in places like flooded wetlands and peatlands. If the previous theories are true, it would mean that loading up soils with these fibrous compounds could be an easy carbon-trapping sink.