Аннотация:Background: The biological activities of dark Chinese teas are largely due to their microbial post-fermentation.Herbal teas are traditional Russian beverages that hold special value, owing to their taste and useful medicinalproperties. However, no data are available in the literature on using microbial post-fermentation for enhancing theirbiological activity. The goal of this work was to demonstrate that the fungus Eurotium isolated from Chinese black teascan be used for the post-fermentation of herbal teas produced from bay willow and apple leaves.Methods: Eurotium cristatum was isolated from brick Chinese tea Fujan and identified using conventional methods ofmicrobiology and molecular biology. Low molecular weight metabolites (phenols, amines, sugars, and amino acids) weredetermined by HPLC. E. cristatum was grown in association with the bacterium Bacillus amyloliquefaciens.Results: It was revealed to exhibit valuable biosynthetic features, such as a lack of mycotoxins, zero antimicrobialactivity, and the capacity to synthesize neuroactive amines. B. amyloliquefaciens displayed a wide spectrum of antibiotic(antimicrobial and antifungal) activities that anifested themselves even with antibiotic-resistant bacteria). While growingon green unfermented tea (Camellia sp.) E. cristatum produced and modified neuroactive amines, such as dopamine,serotonin, and epinephrine. The fungus efficiently grew during the post-fermentation of herbal teas from both bay willowand apple leaves. Even though Camellia leaves substantially differed from bay willow and apple leaves in terms ofphenol content, the growth of E. cristatum on Camellia was also sufficiently good. This suggests that the growth ofEurotium fungi is not influenced by the phenolic compounds. The data obtined on the composition of phenoliccompounds, carbohydrates, and amino acids in the fermented plants and raw material provide evidence that the growthof the fungus proceeds depends on the hydrolysis of high molecular weight phenols and cell biopolymers in thefermented material.Conclusion: Thus, the ability of E. cristatum to grow on plant leaves of significantly different biochemical compositionprovides foundations for new technologies aiming to obtain post-fermented herbal teas with high biological activity thatare enriched in low molecular weight compounds including biogenic amines.