Direct interspecies electron transfer accelerates syntrophic oxidation of butyrate in paddy soil enrichments.

Syntrophic interaction occurs during anaerobic fermentation of organic substances forming methane as the final product. H2 and formate are known to serve as the electron carriers in this process. Recently, it has been shown that direct interspecies electron transfer ( DIET) occurs for syntrophic CH4 production from ethanol and acetate. Here, we constructed paddy soil enrichments to determine the involvement of DIET in syntrophic butyrate oxidation and CH4 production. The results showed that CH4 production was significantly accelerated in the presence of nano Fe3 O4 in all continuous transfers. This acceleration increased with the increase of nano Fe3 O4 concentration but was dismissed when Fe3 O4 was coated with silica that insulated the mineral from electrical conduction. Nano Fe3 O4 particles were found closely attached to the cell surfaces of different morphology, thus bridging cell connections. Molecular approaches, including DNA-based stable isotope probing, revealed that the bacterial S yntrophomonadaceae and G eobacteraceae, and the archaeal M ethanosarcinaceae, M ethanocellales and M ethanobacteriales, were involved in the syntrophic butyrate oxidation and CH4 production. Among them, the growth of G eobacteraceae strictly relied on the presence of nano Fe3 O4 and its electrical conductivity in particular. Other organisms, except M ethanobacteriales, were present in enrichments regardless of nano Fe3 O4 amendment. Collectively, our study demonstrated that the nano Fe3 O4-facilitated DIET occurred in syntrophic CH4 production from butyrate, and G eobacter species played the key role in this process in the paddy soil enrichments. [ABSTRACT FROM AUTHOR]