Electron Hopping Enables Rapid Electron Transfer between Quinone-/Hydroquinone-Containing Organic Molecules in Microbial Iron(III) Mineral Reduction

• DOI: 10.1021/acs.est.0c02521
• Publication Date: 2020-07-27T19:21:10Z
• Authors: Yuge Bai; Tianran Sun; Largus T. Angenent; Stefan B. Haderlein; Andreas Kappler
• Keywords: Hydroquinone; Electron donor

The mechanism of long-distance electron transfer via redox-active particulate natural organic matter (NOM) is still unclear, especially considering its aggregated nature and the resulting low diffusivity quinone- hydroquinone-containing molecules. Here we conducted microbial iron(III) mineral reduction experiments in which anthraquinone-2,6-disulfonate (AQDS, a widely used analogue for molecules NOM) was immobilized agar to achieve spatial separation between iron-reducing bacteria ferrihydrite mineral. Immobilizing AQDS also limited diffusion, resembled electron-transfer behavior NOM. We found that, although diffusion coefficient AQDS/AH2QDS 10 times lower than water, rate (1.60 ± 0.28 mmol L–1 Fe(II) d–1) comparable both media, indicating existence another that accelerated under diffusive conditions. correlation heterogeneous constant (10–3 cm s–1) (10–7 cm2 fitting well with "diffusion-electron hopping" model, suggesting couple accomplished through combination hopping. Electron hopping increased concentration gradient up 106-fold, largely promoted overall during reduction. Our results are helpful explain mechanisms