Insights into links between redox cycling of dissolved organic matter ranked by molecular weight and methanogen-bacteria symbiosis-driven methane production.

Molecular weight (MW) of dissolved organic matter (DOM) governs its redox capacity, playing pivotal roles in methanogen-bacteria symbiosis-driven CH production. However, the effect of redox capacity of DOM ranked by MW on these symbiotic associations during anaerobic digestion have never been investigated. The electron-donating (EDC) and -accepting capacity (EAC) of DOM with different MW were quantified, elucidating their impacts on bacteria-methanogen symbiosis-driven CH production. By contrast, DOM with 7000 > MW > 14,000 Da constituted the primary contribution to EAC, with an average contribution of 44.63 %. DOM with MW > 14,000 Da emerged as the predominant contributor to EDC, with an average contribution of 49.10 %. Random forest showed that EAC/EDC of DOM ranked by MW was the important factors for methanogenesis by driving shifts in microbial symbiotic relationships. 46 genera (relative abundance of 69.55 %) of microorganisms exhibited robust associations with EAC/EDC. EDC of DOM with 3500 < MW < 7000 Da exerted positive effect on CH by modulating the corporation of Caldicoprobacter, norank_o__TSCOR001-H18, norank_o__MBA03 and Methanobrevibacter. EDC of DOM (7000 < MW < 14,000 Da) promotes CH production by regulating cooperation of Corynebacterium, Pseudomonas and Methanosarcina, Methanothermus. EDC of DOM (MW > 14,000 Da) enhances CH production by modulating cooperation of Ureibacillus, Treponema and methanomassiliicoccus, methanogenium. EAC of DOMs were negatively correlated with CH. This study broadens our knowledge on the intricate process of methanogenesis and holds significant importance in developing a microbial symbiosis regulation strategy based on electron transfer system.