Enhancing electron transfer by magnetite during phenanthrene anaerobic methanogenic degradation

Recently, the potential of magnetite facilitating anaerobic methanogenic degradation of organic matters in natural or engineered microbial ecosystems has been reported. Here, we evaluated the effects of magnetite powder (<5 μm) and nanoFe3O4 powder (50-100 nm) on phenanthrene methanogenic degradation by a mixed consortium enriched from petroleum contaminated soil. The results showed that complete phenanthrene degradation in our enrichment cultures required a syntrophic cooperation between degrading bacteria and methanogens. The addition of magnetite and nanoFe3O4 did not increase the relative abundance of methanogens, but improved phenanthrene degradation rates by 25.92% and 25.99%, and enhanced methane production rates by 21.5% and 20.1%, respectively. Further studies showed that the addition of magnetite and nanoFe3O4 improved electron transporting system (ETS) activities in the enrichment cultures, possibly through serving as electron conduits to facilitate DIET between syntrophic bacteria and methanogens.