The secret to a good cup of tea

Does complex flavour in a cup of tea depend mainly on the tea varieties used to make it? A study published in Current Biology suggests otherwise, finding that the flavours in a cup of tea depend on another key ingredient: the collection of microbes found on tea roots. By altering that assemblage, the authors were able to make better-tasting tea.

“Significant disparities in microbial communities, particularly nitrogen metabolism-related microorganisms, were identified in the roots of tea plants with varying qualities through microbiomics,” said Tongda Xu of Fujian Agriculture and Forestry University in Fujian, China. “Crucially, through the isolation and assembly of a synthetic microbial community from high-quality tea plant roots, we managed to notably enhance the amino acid content in various tea plant varieties, resulting in an improvement in tea quality.”

There is a wealth of genetic resources for growing tea plants in China, but, according to the researchers, it is challenging to improve the quality of tea with molecular genetic breeding. There is interest in finding ways to modify and enhance tea with molecular breeding methods, perhaps by using microbial agents. Earlier studies have revealed that soil microbes living in plant roots affect the way nutrients are taken up and used within plants. The researchers wanted to learn more about how those root microbes affected tea quality.

They found that the microbes affected tea’s uptake of ammonia, which in turn influenced the production of theanine, key to determining a tea’s taste. They also saw variations in the microbes colonising different teas. By comparing tea varieties with different amounts of theanine, they identified a set of microbes that looked promising for altering nitrogen metabolism and boosting theanine levels.

The researchers then constructed a synthetic microbial community, dubbed SynCom, that mirrored the one found in association with Rougui, a high-theanine tea variety. When SynCom was applied to tea roots, it boosted theanine levels. The microbes also allowed Arabidopsis thaliana, a plant commonly used in basic biological studies, to better tolerate low nitrogen conditions.

“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,” said study co-author Wenxin Tang. “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. Furthermore, this effect is particularly pronounced in low-nitrogen soil conditions.”

The findings suggest that synthetically produced microbial communities could improve teas, especially when grown in nitrogen-deficient soil conditions. Tea trees require lots of nitrogen, so this discovery may help reduce the use of chemical fertiliser while promoting tea tree quality.

The researchers now plan to further optimise SynCom and assess its use in field trials. They also hope to learn more about how root microbes affect other secondary metabolites in tea trees.

Image credit: iStock.com/Delmaine Donson