Abstract
Potential for interspecies hydrogen transfer within paddy soil enrichments obtained via addition of magnetite nanoparticles and ethanol (named as PEM) was investigated. To do this, PEM derived from rice field of Hangzhou (named as PEM-HZ) was employed, because it offered the best methane production performance. Methane production and Fe (III) reduction proceeded in parallel in the presence of magnetite. Inhibition experiments with 2-bromoethane sulfonate (BES) or phosphate showed that interspecies hydrogen transfer and Fe (III) reduction also occurred in methane production from ethanol. 16S rRNA-based Illumina sequencing results showed that Dechloromonas, Thauera, Desulfovibrio and Clostridium were the dominant putative Fe (III) -reducers, and that hydrogenotrophic Methanobacterium accounted for about 88% of the total archaeal community. These results indicated that magnetite nanoparticles that acted as electron acceptor could facilitate rapid oxidation of ethanol by members of the Fe (III) -reducers in PEM-HZ and establishment of the syntrophic relationship of Fe (III) -reducers with Methanobacterium via interspecies hydrogen transfer. Our results could offer a model to understand the microbial interaction with magnetite from a novel angle during methanogenesis.
Highlights
Preliminary experiment significant H2 production and Clostridia were detected in paddy soil amended with magnetite and ethanol
The accumulation of volatile fatty acids (VFAs) in PEC-HZ indicated that parts of carbon flux of ethanol might shift towards carboxylic acid production rather than methane production due to the decreased methanogen populations (Fig. 1b)
The results showed that magnetite addition to paddy soil altered the microbial ecosystem, accelerated methane production, and led to the dominance of hydrogenotrophic methanogenesis
Summary
Preliminary experiment significant H2 production and Clostridia were detected in paddy soil amended with magnetite and ethanol. In syntrophic methanogenesis, ethanol oxidation is thermodynamically unfavorable (Δ G0′ = + 9.6 kJ/mol) and can occur only when a very low H2 pressure is kept by hydrogen-scavenging methanogens[11]. In the light of this context, we hypothesized that magnetite could facilitate methane production from ethanol in other manners in addition to acting as a conduit of electrons. To test this hypothesis, paddy soil enrichments obtained in the presence of magnetite nanoparticles and ethanol (named as PEM) were firstly established in this work.
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