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Background  Caffeine, theobromine and theophylline are main purine alkaloid in tea. Theophylline is the downstream metabolite and it remains at a very low level in  Camellia sinensis . In our previous study,  Aspergillus sydowii  could convert caffeine into theophylline in solid-state fermentation of pu-erh tea through  N -demethylation. In this study, tea-derived fungi caused theophylline degradation in the solid-state fermentation. The purpose of this study is identify and isolate theophylline-degrading fungi and investigate their application in production of methylxanthines with theophylline as feedstock through microbial conversion.    Results  Seven tea-derived fungi were collected and identified by ITS, β-tubulin and calmodulin gene sequences,  Aspergillus ustus ,  Aspergillus tamarii ,  Aspergillus niger  and  A. sydowii  associated with solid-state fermentation of pu-erh tea have shown ability to degrade theophylline in liquid culture. Particularly,  A. ustus  and  A. tamarii  could degrade theophylline highly significantly (p < 0.01). 1,3-dimethyluric acid, 3-methylxanthine, 3-methyluric acid, xanthine and uric acid were detected consecutively by HPLC in  A. ustus  and  A. tamarii , respectively. The data from absolute quantification analysis suggested that 3-methylxanthine and xanthine were the main degraded metabolites in  A. ustus  and  A. tamarii , respectively. 129.48 ± 5.81 mg/L of 3-methylxanthine and 159.11 ± 10.8 mg/L of xanthine were produced by  A. ustus  and  A. tamarii  in 300 mg/L of theophylline liquid medium, respectively.    Conclusions  For the first time, we confirmed that isolated  A. ustus ,  A. tamarii  degrade theophylline through  N -demethylation and oxidation. We were able to biologically produce 3-methylxanthine and xanthine efficiently from theophylline through a new microbial synthesis platform with  A. ustus  and  A. tamarii  as appropriate starter strains.

Isolation, characterization and application of theophylline-degrading Aspergillus fungi