Fig. 3: Characterization of coculture biofilm and produced organic substances.

a Dense biofilm in culture bottle (the inset image shows the picture of culture bottle). Optical microscopy image (b) and FISH image (c) with M. b (green-fluorescing probe) and PCC6803 (red, autofluorescence); representative of 10 images. d Schematic illustration for biotic methanogenesis driven by intermediates with PCC6803-M. b-Fe-EDTA. e Possible organic substances generated via ROS oxidation. gCOSY (f) and gHMBC (g) superimposed aqueous 600-MHz NMR spectra of supernatants after the syntrophic coculture for 6 days (black), 0.1 M lactate (green), 0.1 M acetate (red), 0.1 M pyruvate (blue), and 0.1 M methanol (orange yellow). The red circled peak in (g) is assigned to acetate, the blue circled peak is assigned to pyruvate, and the orange yellow circled peak is assigned to methanol. h Variation of acetate concentration under a light-dark cycle of 4 h–20 h. The gray color presents the dark period. Data are presented as mean values ± SD derived from n = 3 independent experiments. Scale bars: 1 μm in (a), 10 μm in (b), and 10 μm in (c). Source data are provided as a Source Data file.