Fungal material: Houttuynia cordata was grown in a local garden at Willich, Germany. Fresh roots were harvested in April 2016 and washed with sterilized water, surface sterilized with 70% ethanol for 1 min, and cut into small pieces (around 1 × 1 × 1 cm) using a flame sterilized blade. These pieces were put on malt agar plates (15 g/L malt extract, 15 g/L agar, and 0.2 g/L chloramphenicol in distilled water, pH 7.4-7.8 with sodium hydroxide or hydrochloric acid), and then incubated at room temperature for several days. Fermentation and co-cultivation: Fermentation of the fungus was conducted in 11 Erlenmeyer flasks on solid rice medium (100 g rice in 110 mL water followed by autoclaving) at 20 ℃ at static conditions. After 33 days each flask was extracted with 600 mL EtOAc. Co-cultivation experiment with Bacillus subtilis (ATCC168) was conducted on solid rice medium. A total of 15 flasks was prepared (5 axenic fungal cultures as controls, 5 co-cultures with bacteria and 5 axenic bacterial cultures as controls). After addition of 10 mL bacteria solution to each flask, the flasks were incubated at 30 ℃ for three days. Then a constant number of pieces from agar plates containing Trichocladium sp. were transferred to the co-culture flasks. All flasks were inoculated at 20 ℃ under static conditions. After 33 days 600 mL EtOAc was added to each flask in order to terminate the cultivation. OSMAC experiments: In addition to rice, peas (Pisum sativum, from Mullers Muhle, Germany) were used as medium (100 g of peas in 110 mL of H₂O followed by autoclaving). The cultivation procedure was the same as described for cultivation on rice medium. For the feeding experiment using tryptophan, the rice medium was spiked with 2% tryptophan prior to autoclaving.

Addition of tryptophan to the rice medium which was done trying to mimic the higher protein content of peas vs. rice caused the accumulation of the new compound 13-N-(2-Carboxyphenyl)colletoketol which in addition to colletoketol includes anthranilic acid, the latter probably being a fungal biotransformation product of added tryptophan.