Acetate oxidation by syntrophic association between Geobacter sulfurreducens and a hydrogen-utilizing exoelectrogen

Abstract

Anodic microbial communities in acetate-fed microbial fuel cells (MFCs) were analyzed using stableisotope probing of 16S rRNA genes followed by denaturing gradient gel electrophoresis. The results revealed that Geobacter sulfurreducens and Hydrogenophaga sp. predominated in the anodic biofilm. Although the predominance of Geobacter sp. as acetoclastic exoelectrogens in acetate-fed MFC systems has been often reported, the ecophysiological role of Hydrogenophaga sp. is unknown. Therefore, we isolated and characterized a bacterium closely related to Hydrogenophaga sp. (designated strain AR20). The newly isolated strain AR20 could use molecular hydrogen (H 2 ), but not acetate, with carbon electrode as the electron acceptor, indicating that the strain AR20 was a hydrogenotrophic exoelectrogen. This evidence raises a hypothesis that acetate was oxidized by G. sulfurreducens in syntrophic cooperation with the strain AR20 as a hydrogen-consuming partner in the acetate-fed MFC. To prove this hypothesis, G. sulfurreducens strain PCA was cocultivated with the strain AR20 in the acetate-fed MFC without any dissolved electron acceptors. In the coculture MFC of G. sulfurreducens and strain AR20, current generation and acetate degradation were the highest, and the growth of strain AR20 was observed. No current generation, acetate degradation and cell growth occurred in the strain AR20 pure culture MFC. These results show for the first time that G. sulfurreducens can oxidize acetate in syntrophic cooperation with the isolated Hydrogenophaga sp. strain AR20, with electrode as the electron acceptor.

Syntrophy in microbial fuel cells

“…For the co-culture to be syntrophic, it would require that G. sulfurreducens ceases to be an electrogen, or more precisely ceases to be able to use electrodes as electron acceptor. The data put forward by Kimura and Okabe (2013) provide no evidence that this indeed the case, though they do indicate that G. sulfurreducens PCA benefits from the presence of Hydrogenophaga sp. strain AR20.…”

“…That is, until recently. Earlier this year Kimura and Okabe (2013) reported that Geobacter sulfurreducens PCA can oxidize acetate in what the authors labelled 'a syntrophic cooperation' with Hydrogenophaga sp. strain AR20 in conjunction with an electrode as the final electron acceptor.…”

Isolation and characterization of a bacterial strain Hydrogenophaga sp. PYR1 for anaerobic pyrene and benzo[a]pyrene biodegradation

“…29,30 However, it was reported that H. intermedia and H. atypica are unable to grow chemolithoautotrophically using hydrogen gas, and only a few organic compounds can be used as sole carbon sources.…”

Optimization of Bioelectricity Generation in Constructed Wetland-Coupled Microbial Fuel Cell Systems

“…Organic matter can be used as a renewable resource to generate electrons and protons via electrochemically active bacteria in MFCs [4][5][6]. Protons are released into solution and electrons are produced at the anode; subsequently, at the interface of the cathode, electrons pass through the outer circuit before they can reach the cathode and combine with electron acceptors [7,8].…”