Fig. 1: Scheme of incubation experiments and formation of methane and carbon dioxide from long-chain alkanes.

Scheme of incubation experiments (a), concentration of methane (b) and carbon dioxide (c), carbon isotope of methane (d) and carbon dioxide (e), and concentration of ¹³C-labled methane (f) and carbon dioxide (g) in the cultures. r1 and r2 represent two replicates. The samples were incubated at 60 °C in Dec. 2021. Alkane groups: two bottles of slurry samples with the addition of 1% (volume/volume) tetradecane and fresh medium (with NaHCO₃) during the initial cultivation; after 228 days culturing, 1% (volume/volume) tetradecane and 20% (v/v) fresh medium (with NaHCO₃) were supplemented; after 386 days culturing, 0.1% (v/v) hexadecane and 20% (v/v) fresh medium (with NaHCO₃) were supplemented, and the headspace in bottles was replaced with nitrogen; at day 614, after mixing the two samples thoroughly, divide the mixture into two equal parts, 0.1% (v/v) hexadecane and 100% (v/v) fresh medium (without NaHCO₃) were supplemented, the headspace in the bottles was replaced with nitrogen; after 676 days culturing, 0.1% (v/v) hexadecane and 10% (v/v) fresh medium (without NaHCO₃) were supplemented, and the headspace in the bottles was replaced with nitrogen; after 750 days culturing, 0.1% (v/v) 1,2-¹³C-labeled hexadecane and 10% (v/v) fresh medium (without NaHCO₃) were supplemented, and the headspace in the bottles was replaced with nitrogen.