Melatonin Production Optimization in Bacteria

To measure the production of melatonin, bacterial cells were cultivated in deep-well plates in glucose slow-release (GSR) medium mimicking fed-batch fermentation at 30°C. 1 L of GSR medium contains 15 g of Maltodextrin (dextrose equivalent 4.0–7.0, Sigma-Aldrich), 200U of Amyloglucosidase (Sigma-Aldrich, ∼70 U/mg) for glucose release, 40 g of MES monohydrate (Sigma-Aldrich), 1.2 g of K₂HPO₄, 7 g of Ammonium sulfate, 120 mg of Sodium citrate, 8 mg of ZnCl₂, 12 mg of FeSO₄⋅7H₂O, 9 uM of CaCl₂, 12.5 mM of MgSO₄⋅7H₂O, as well as trace elements and vitamins. The media pH was adjusted to 6.4. The medium was supplemented with 500 mg/L tryptophan, 50 mg/L kanamycin, and 100 mg/L ampicillin. The bacterial cells were cultivated at 30°C in M9 medium supplemented with 0.5% glucose for 24 h. The precultures were diluted 100 times into the GSR medium and cultured at 30°C. After 24 h, the supernatant was collected by filtering the broth with 0.2 μm filters (Pall, New York, United States). The concentration of melatonin in the supernatant was determined by HPLC as previously described (Luo et al., 2019 (link)).