Mixing up root microbes can boost tea’s flavor

Dosing dirt with nitrogen-metabolizing bacteria boosted synthesis of a taste-enhancing amino acid

Tea farm in China

The mountainous region of China known as Wuyishan, shown here, is a renowned source of rougui and other oolong teas.

Wei Xin

Researchers may have gotten to the root of tea’s soothing effect.

The quality of a cup of chai can be enriched by modifying the microbial community that populates the plant’s roots, researchers report February 15 in Current Biology. The secret is to inoculate roots with bacteria that boost the synthesis of the amino acid theanine.

There’s something in tea that helps us wind down, says Zhenbiao Yang, a plant cell biologist at the Shenzhen Institute of Advanced Technology in China. Some studies suggest that the “chemical that helps you sleep is theanine,” he says. What’s more, theanine infuses tea with umami, a taste often described a savoriness, he says.

Yang and colleagues analyzed the microbial communities inhabiting the roots of two oolong tea plant varieties: a sweet, low-theanine cultivar called maoxie and a cinnamony, high-theanine variety called rougui. On the rougui roots, they found more microbes that metabolize nitrogen, a nutrient tea plants convert into theanine.

The researchers then isolated 21 bacterial strains from rougui roots to concoct an experimental microbial medley, which they called SynCom. They disinfected the roots of seedlings of several tea plant varieties, grew them in sterilized vermiculite soil for a few weeks, and then inoculated soils with live or dead SynCom. They also added a nutrient solution that was either low or high in nitrogen.

After 20 days, Yang’s team found that the addition of live SynCom boosted theanine levels in each of the varieties. The effect was especially pronounced under the lower nitrogen conditions — leaves of maoxie plants inoculated with living SynCom contained almost 0.007 milligrams per gram of theanine, 0.005 mg/g higher than maoxie inoculated with dead SynCom.

The next step will be to refine SynCom to facilitate its production and distribution, Yang says. “If we have only like one or two [strains], it will be really easy.”

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