Fig. 6: Extracellular electron enables DMAs and methanol-derived methanogenesis by paddy soils.

One gram of each paddy soils of CZ (A), TC (B), and FY (C) was inoculated into 5 mL methanol medium amened with 20 μM DMAs and 2 μM ¹³C-DMAs, and gas mixture including 30% CO to inhibit hydrogenase. ¹³CH₄ (red bar) and ¹³CO₂ (blue bar) in the headspace were determined using GC–IRMS. Each 9 g paddy soils sampled from CZ and FY were added to cathodic chambers of H-cell containing 90 mL modified MM medium with about 1800 μmol methanol. The cathodic potential was set at −0.4 V. Methane content (D) in the headspace of cathodic chambers with (closed symbols) or without (open symbols) power supply was monitored during 12 day-incubation at 30 °C. Current consumptions (E) of the cathodic chamber with power supply as A were monitored during 12 days incubation, and a chamber without inoculation of paddy soils was included as an abiotic control. Duplicate experiments were performed, and the means and standard deviations are shown. Relative abundances of methanogens of cathodic enrichments with (+) or without (−) power supply were determined via archaea specific 16S rRNA ampilcon sequeccing (F).