Abstract
Syntrophic oxidation of butyrate is catabolized by a few bacteria specialists in the presence of methanogens. In the present study, a highly enriched butyrate-oxidizing consortium was obtained from a wetland sediment in Tibetan Plateau. During continuous transfers of the enrichment, the addition of magnetite nanoparticles (nanoFe3O4) consistently enhanced butyrate oxidation and CH4 production. Molecular analysis revealed that all bacterial sequences from the consortium belonged to Syntrophomonas with the closest relative of Syntrophomonas wolfei and 96% of the archaeal sequences were related to Methanobacteria with the remaining sequences to Methanocella. Addition of graphite and carbon nanotubes for a replacement of nanoFe3O4 caused the similar stimulatory effect. Silica coating of nanoFe3O4 surface, however, completely eliminated the stimulatory effect. The control experiment with axenic cultivation of a Syntrophomonas strain and two methanogen strains showed no effect by nanoFe3O4. Together, the results in the present study support that syntrophic oxidation of butyrate is likely facilitated by direct interspecies electron transfer in the presence of conductive nanomaterials.
Highlights
Methane is an end product of anaerobic food web degrading organic substances in anoxic habitats
The production of CH4 occurred without a lag in the initial two transfers indicating the readily activity of butyrate oxidation in this wetland sediment (Supplementary Figures S1A,B)
These results indicated that butyrate was stoichiometrically converted to CH4 and CO2 in the first two transfers, while thereafter the aceticlastic methanogens were lost and CH4 was only produced from CO2 reduction by the electrons released from butyrate oxidation
Summary
Methane is an end product of anaerobic food web degrading organic substances in anoxic habitats. Under methanogenic conditions where the electron donors other than protons and CO2 are absent, the complicated organic substances undergo fermentation producing short-chain alcohols and fatty acids as intermediate products (Drake et al, 2009). Secondary fermenters metabolize these products by discharging electrons to protons forming H2 or formate, which are used by methanogens. Amino acids like alanine was found to serve as a supplemental carrier for interspecies electron transfer (Walker et al, 2012)
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