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

Abstract

Summary: Syntrophic interaction occurs during anaerobic fermentation of organic substances forming methane as the final product. H 2 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 CH 4 production from ethanol and acetate. Here, we constructed paddy soil enrichments to determine the involvement of DIET in syntrophic butyrate oxidation and CH 4 production. The results showed that CH 4 production was significantly accelerated in the presence of nano Fe 3 O 4 in all continuous transfers. This acceleration increased with the increase of nano Fe 3 O 4 concentration but was dismissed when Fe 3 O 4 was coated with silica that insulated the mineral from electrical conduction. Nano Fe 3 O 4 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 CH 4 production. Among them, the growth of G eobacteraceae strictly relied on the presence of nano Fe 3 O 4 and its electrical conductivity in particular. Other organisms, except M ethanobacteriales , were present in enrichments regardless of nano Fe 3 O 4 amendment. Collectively, our study demonstrated that the nano Fe 3 O 4 ‐facilitated DIET occurred in syntrophic CH 4 production from butyrate, and G eobacter species played the key role in this process in the paddy soil enrichments.