Quantitative analysis of acetate oxidation in the presence of iron in a thermophilic methanogenic reactor

In natural and engineered anaerobic ecosystems, syntrophic oxidation of short-chain fatty acid is one of the key factors and interspecies electron transfer mechanisms between bacteria and archaea play a pivotal role. Growing evidence suggests that microorganisms have the capability to promote interspecies electrons transfer in a more direct manner. In the current study, three different types of iron oxides were used to thermophilic anaerobic reactors (at 50 °C), quantitative polymerase chain reaction and 16S rRNA sequencing technique were applied to investigate the relation between iron reduction bacteria and syntrophic acetate oxidation bacteria. Experiment results showed that goethite and hematite promoted the methane production and generation rate and partially relieved the negative effects of H2. The syntrophic relation between Syntrophaceticus and Methanobacterium worked with a direct interspecies electron transfer model rather than interspecies hydrogen transfer in goethite and hematite dosed reactors. The gene copies of Syntrophaceticus predominated over that of Geobacter. Theoretical calculations revealed that the rates of iron oxide mediated interspecies electron transfer among syntrophic partners were 105-106 times higher than those attainable via interspecies H2 transfer.