Electron transfer from Geobacter sulfurreducens to mixed methanogens improved methane production with feedstock gases of H2 and CO2

In order to solve problems of poor utilization of H-2 and CO2 in biomethane conversion with mixed methanogens due to multi-channel competition and nondirectional electron transfer, Geobacter sulfurreducens were cocultured with mixed methanogens to promote oriented metabolic pathway of H-2 and CO2 to produce CH4. When inoculation volume ratio of G. sulfurreducens to mixed methanogens was 2:4, CH4 yield increased to 0.24 mL/ml H-2 (close to the maximum theoretical yield of 0.25 mL/ml H-2) and conversion efficiency of H2 to CH4 increased from 72 to 96%. Electrochemical detection and three-dimensional fluorescence spectra showed that the co-culture system had an increased metabolic capacity and spectral intensity of fulvic acid-like compounds was enhanced, which mediated direct interspecific electron transfer to produce CH4. The 16S rRNA gene sequencing showed that relative abundance of G. sulfurreducens and Methanoculleus increased, indicating an established syntrophic relationship between G. sulfurreducens and Methanoculleus.

Automated summary

This study investigated the use of co-culturing Geobacter sulfurreducens with mixed methanogens to address the issue of poor utilization of H-2 and CO2 in biomethane conversion. The results showed that, with a specific inoculation volume ratio, there was a significant improvement in methane production and H2 conversion efficiency. Furthermore, electrochemical detection and fluorescence spectra analysis revealed an enhanced metabolic capacity and the ability for direct interspecific electron transfer to produce CH4 in the co-culture system. Additionally, gene sequencing demonstrated the establishment of a mutualistic relationship between G. sulfurreducens and Methanoculleus.