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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]

The identification of dominant microbes in anaerobic mercury (Hg) methylation, methylmercury (MeHg) demethylation, and methane oxidation as sulfate-reducing bacteria, methanogens or, probably, anaerobic methanotrophic archaea (ANMEs) is of great interest. To date, however, the interrelationship of bacteria and archaea involved in these processes remains unclear. Here, we demonstrated the dynamics of microorganisms participating in these processes. Anaerobic fixed-bed reactors were operated with swine manure and sludge to produce methane stably, and then, sulfate (reactor C), sulfate and Hg(II) (reactor H), and sulfate and MeHg (reactor M) were added, and the reactors were operated for 120 d, divided equally into four periods, P1–P4. The bacterial compositions changed nonsignificantly, whereas Methanosaeta in reactors H and M decreased significantly, revealing that it was irrelevant for Hg transformation. The abundances of Syntrophomonadaceae , Methanoculleus , Candidatus Methanogranum and Candidatus Methanoplasma increased continuously with time; these species probably functioned in these processes, but further evidence is needed. Desulfocella and Desulfobacterium dominated first but eventually almost vanished, while the dominant archaeal genera Methanogenium , Methanoculleus and Methanocorpusculum were closely related to ANME–1 and ANME–2. PLS-DA results indicated that both bacteria and archaea in different periods in the three reactors were clustered separately, implying that the microbial compositions in the same periods were similar and changed markedly with time. [Display omitted] • Methanosaeta decreased significantly after adding Hg and was unrelated to Hg transformation. • Desulfocella and Desulfobacterium dominated first but finally almost vanished. • The dominant archaeal genera were closely related to ANME–1 and ANME–2. • Microbes in different periods clustered separately, showing a significant change with time. [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]