A good cup of tea depends on very tiny bugs

What makes a perfect cup of tea? According to a team of Chinese scientists, the answer is not the right pot, temperature, or the sacrilegious addition of salt – it’s microbes.

The research team has found that the composition of microbes at the roots of a tea plant has a huge impact on the tea’s quality and taste.

Bacteria, fungi, and other tiny creatures in the soil affect how much nitrogen the plant can absorb, which decides the molecules that end up in your cup.

The research, published in Current Biology, could lead not only to improved tea quality, but also improve the nutritional value of other crops like rice.

One of the big deciders in tea quality and taste is the compound theanine, which is a type of amino acid. Like all amino acids, it’s nitrogen-based.

The researchers investigated the root microbiomes of varieties of Camellia sinensis plants, which grow tea leaves. They looked at varieties which yield both high theanine levels, and low theanine.

Tea plantation
Tea Mountain from Wuyishan, Fujian, China. Credit: Wei Xin

“Significant disparities in microbial communities, particularly nitrogen metabolism-related microorganisms, were identified in the roots of tea plants with varying qualities through microbiomics,” says co-author Tongda Xu, a researcher at the Fujian Agriculture and Forestry University in China.

The researchers found that microbes around the roots of the high-theanine plants made the plants absorb more ammonia, which means more nitrogen gets into the plant.

They then designed a synthetic microbial community based on their analysis, which they thought would make the most theanine-heavy tea.

“We managed to notably enhance the amino acid content in various tea plant varieties, resulting in an improvement in tea quality,” says Xu.

The researchers called their community SynCom21. They initially thought it would be useful for improving low quality tea varieties, but they tested it out on high-quality varieties too.

Tea plantation in mountains
Tea Mountain from Wuyishan, Fujian, China. Credit: Wei Xin

“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 [ammonia uptake] promoting effect on certain high-quality tea varieties,” says co-author Wenxin Tang, also at the Fujian Agriculture and Forestry University.

“Furthermore, this effect is particularly pronounced in low-nitrogen soil conditions.”

This means that the synthetic microbial community could lower the need for fertilisers on tea trees.

The researchers also tried SynCom21 out on another plant, Arabidopsis thaliana or thale cress, which is often used as a plant model in scientific studies. The microbes also helped this plant absorb more nitrogen.

“This suggests that the ammonium nitrogen uptake-promoting function of SynCom21 may be applicable to various plants, including other crops,” says Xu.

The team is now planning to take their synthetic microbial community to field trials, to see how it works in a less controlled environment.

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