Endophytic bacterium V4 from albino tea plant enhances umami taste as well as flowery and roasted aromas in dried tea.

The application of microbial fertilizers in tea cultivation has emerged a promising strategy to enhance tea quality and promote sustainable agricultural practices. However, the underlying mechanism remains unclear. In this study, the impacts of endophytic bacteria V4 on tea fresh leaves and dried tea were investigated. The results demonstrated that astringency in V4 sample was significantly reduced, while the umami and sweetness tastes, along with flowery and roasted aromas were significantly enhanced compared to the SW sample. Analysis of key quality-related compounds revealed a significant decrease in tea polyphenols and catechins, accompanied by a marked increase in free amino acids and soluble sugars. Evaluation of aroma characteristic impact (ACI) values of key volatile compounds revealed that β-ionone, 2-ethyl-3,5-dimethylpyrazine, 2-ethyl-3,6-dimethylpyrazine and 2,3-diethyl-5-methylpyrazine in V4 sample were significantly higher than those in SW sample. Transcriptomic analysis indicated downregulation of key catechin biosynthesis genes (such as CsLAR, CsANS and CsSCPL) in tea leaves treated with V4, while theanine biosynthetic genes such as CsAlaDC and CsTS were upregulated. This study provides a sustainable and innovative cultivation strategy for significantly improving tea flavor and enhancing product quality.