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[Display omitted] • Acetoclastic pathway was most important in low-temperature MES. • Methahnosarcina and Methanothrix were enriched in DC and SC reactor, respectively. • Electroactive bacteria Syntrophomonas , Pseudomonas and Bacteroides were dominated. • The single-chamber MES achieve acetate to acetyl-CoA by acetate-CoA ligase. • The dual-chamber MES was by acetate kinase and phosphate acetyltransferase. In this study, single-chamber and dual-chamber Microbial electrosynthesis (MES) with carbon fiber brushes as electrodes were operated at 15°C to compare and analyze the difference in methanogenic performance. Metatranscriptomic analysis showed that the relative abundance of electroactive microorganisms Syntrophomonas , Pseudomonas and Bacteroides in each group exceeded 90%, while the abundance of Geobacter was less than 4%. Acetoclastic methanogens Methahnosarcina was more enriched in dual-chamber MES (61.74%~70.42%), and Methanothrix showed higher abundance in single-chamber MES (33.44%~51.71%). Methahnosarcina and Methanothrix could interact with electroactive microorganisms to improve the electron transfer efficiency through direct interspecies electron transfer (DIET). Analysis of the methane metabolic pathways of low-temperature MES found acetoclastic pathway was domination, and single-chamber MES achieved acetate to acetyl-CoA through acetate-CoA ligase (EC: 6.2.1.1), whereas dual-chamber MES was by acetate kinase (EC: 2.7.2.1) and phosphate acetyltransferase (EC: 2.3.1.8). These results are beneficial to further research on the treatment of low-temperature wastewater. [ABSTRACT FROM AUTHOR]

• Cumulative methane production was not significantly different between the two reactors. • Acidogens and H 2 -producing bacteria were higher in the single-chamber MES. • Fermentation bacteria and methanogens were concentrated in the dual-chamber MES. • In dual-chamber MES, it was primarily acetoclastic methanogenic pathway. • In single-chamber MES cathode, hydrogenotrophic methanogenic pathway dominated. Microbial electrosynthesis (MES) is an advanced technology for efficient treatment of organic wastewater and recovery of new energy, with the advantages and disadvantages of single-chamber and dual-chamber MES reactors being less understood. Therefore, we explored the effects of single-chamber and dual-chamber structures on the methane production performance and microbial community structure of MES. Results indicated that methane concentration and current density of single-chamber MES were higher than those of dual-chamber MES, and the system stability was better, while chemical oxygen demand (COD) removal rate and cumulative methane production were not significantly different. Analysis of microbial community structure showed the abundance of acidogens and H 2 -producing bacteria was higher in single-chamber MES, while fermentation bacteria and methanogens was lower. The abundance of methanogens of dual-chamber MES (21.74–24.70%) was superior to the single-chamber MES (8.23–10.10%). Moreover, in dual-chamber MES, methane was produced primarily through acetoclastic methanogenic pathway, while in single-chamber MES cathode, methane production was mainly by hydrogenotrophic methanogenic pathway. Information provided will be useful to select suitable reactors and optimize reaction design. [ABSTRACT FROM AUTHOR]

[Display omitted] • The methanogenic performance was better when the applied voltage was 0.8 V. • Clostrodium and Methanosaeta were the most dominant microbial populations. • MES-Cathode was more tolerant to the effects of higher NH 4 +-N concentration. • CH 4 was produced mainly via hydrogenotrophic methanogenic pathway in MES-Cathode. • MES produced CH 4 via SOAB, hydrogenotrophic archaea if acetoclastic pathway curbed. Microbial electrosynthesis (MES) has great potential for energy and resource recovery in wastewater treatment and has therefore gradually become a popular research topic. In this study, MES with an applied voltage (0.6 V, 0.8 V and 1.0 V) significantly improved biogas production (36.0 %, 52.3 %, and 59.1 %, respectively) compared with the control (without electrodes). Analysis of microbial community structure revealed that Clostridium and Methanosaeta had the highest relative abundance in all reactors. The abundances of Acetivibrio and Geobacter dominated the bioanode, and methane production was mainly mediated by the acetoclastic methanogenic pathway. On the biocathode, the abundances of Methanolinea and Methanothermobacter were higher than those of other microbes, and methane was produced primarily through the hydrogenotrophic methanogenic pathway. When the acetoclastic methanogenic pathway in the biocathode was inhibited, MES could efficiently produce methane through other pathways. In addition, MES was more tolerant to the effects of high NH 4 +-N concentrations than anaerobic digestion (AD). These results suggest that applying voltage to the bioanode and biocathode could better improve the efficiency of methane production. [ABSTRACT FROM AUTHOR]