3-Methylxanthine production through biodegradation of theobromine byAspergillus sydowiiPT-2

Background Methylxanthines, including caffeine, theobromine and theophylline, are natural and synthetic compounds in tea, which could be metabolized by certain kinds of bacteria and fungi. Previous studies confirmed that several microbial isolates from Pu-erh tea could degrade and convert caffeine and theophylline. We speculated that these candidate isolates also could degrade and convert theobromine through N-demethylation and oxidation. In this study, seven tea-derived fungal strains were inoculated into various theobromine agar medias and theobromine liquid mediums to assess their capacity in theobromine utilization. Related metabolites with theobromine degradation were detected by using HPLC in the liquid culture to investigate their potential application in the production of 3-methylxanthine. Results Based on theobromine utilization capacity,Aspergillus nigerPT-1,Aspergillus sydowiiPT-2,Aspergillus ustusPT-6 andAspergillus tamariiPT-7 have demonstrated the potential for theobromine biodegradation. Particularly,A. sydowiiPT-2 andA. tamariiPT-7 could degrade theobromine significantly (p < 0.05) in all given liquid mediums. 3,7-Dimethyluric acid, 3-methylxanthine, 7-methylxanthine, 3-methyluric acid, xanthine, and uric acid were detected inA. sydowiiPT-2 andA. tamariiPT-7 culture, respectively, which confirmed the existence of N-demethylation and oxidation in theobromine catabolism. 3-Methylxanthine was common and main demethylated metabolite of theobromine in the liquid culture. 3-Methylxanthine inA. sydowiiPT-2 culture showed a linear relation with initial theobromine concentrations that 177.12 +/- 14.06 mg/L 3-methylxanthine was accumulated in TLM-S with 300 mg/L theobromine. Additionally, pH at 5 and metal ion of Fe(2+)promoted 3-methylxanthine production significantly (p < 0.05). Conclusions This study is the first to confirm thatA. sydowiiPT-2 andA. tamariiPT-7 degrade theobromine through N-demethylation and oxidation, respectively.A. sydowiiPT-2 showed the potential application in 3-methylxanthine production with theobromine as feedstock through the N-demethylation at N-7 position.