From the strength of black and Earl Grey teas to the soothing and light flavors of herbal and green teas, the little plants brewed in this millennia-old beverage have endless variety. However, the complexity and quality of their flavor could depend on something even smaller than the leaves themselves. A study published February 15 in the journal Current Biology found that the microbes at the tea’s roots may make high-quality tea even better.   

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Of the roughly 15 billion pounds of tea that were consumed in 2022, close to one-third was grown in China. The country is believed to be tea’s birthplace, with the earliest credible record of tea drinking dating back to the Third Century CE, but it could be even older. 

Some previous studies noted that the soil microbes living at the roots of plants affect the way that nutrients are absorbed and used by the plant to grow and flourish. However, improving the quality of tea leaves in the lab by genetically altering the plants is challenging and difficult to achieve in the lab. According to the team from this study, there is a vested interest in finding other ways to modify and enhance tea, potentially with microbial agents.

Agriculture photo
Tea Mountain in Wuyishan, Fujian, China. CREDIT: Wei Xin.

In this new study, a team in China wanted to learn more about how specifically root microbes will affect tea quality. They studied 17 different tea varieties and monitored how the microbes in the tea roots affected how well they take in ammonia. This ammonia intake then influenced how well an amino acid called theanine was produced. Theanine is key to determining the taste of tea.

The researchers also noticed variations in the microbes that were colonizing different teas. Comparing tea varieties with different amounts of theanine within its leaves helped them pinpoint the set of microbes that could boost theanine levels for better tea flavor. 

Next, the team built a synthetic microbial community called SynCom that was similar to a natural microbial community found with a high-theanine tea variety called Rougui. When they added the SynCom microbes to tea roots, theanine levels increased and the flavor complexity and strength also improved. 

“The initial expectation for the synthetic microbial community derived from high-quality tea plant roots was to enhance the quality of low-quality tea plants,” study co-author and Fujian Agriculture and Forestry University plant biologist Wenxin Tang said in a statement. “However, to our astonishment, we discovered that the synthetic microbial community not only enhances the quality of low-quality tea plants but also exerts a significant promoting effect on certain high-quality tea varieties.”

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These findings suggest that using synthetically produced microbial communities like SynCom could improve teas. This could particularly help when teas are grown in soils low in nitrogen. Tea trees require a lot of nitrogen, and using microbial communities like the one from this study could help reduce the use of chemical fertilizers while simultaneously promoting the quality of tea trees. The team also believes that this could be applied to a wide variety of crops, since the microbes also allowed a plant commonly used in basic biological studies called Arabidopsis thaliana, to tolerate low-nitrogen conditions in the soil.

“Based on our current experimental findings, the inclusion of the SynCom21 microbial community has not only improved the absorption of ammonium nitrogen in different tea varieties but also enhanced the uptake of ammonium nitrogen in Arabidopsis thaliana,” study co-author and Fujian Agriculture and Forestry University plant biologist Tongda Xu said in a statement. “This suggests that the ammonium nitrogen uptake-promoting function of SynCom21 may be applicable to various plants, including other crops.”

According to the team, SynCom could help grow rice with higher yields and protein content with future study. They plan to further study how this synthetic microbial community can be used in field trials, and learn more about how root microbes affect tea trees.