A novel mechanism of electron transfer from microorganisms to insoluble iron phases

微生物铁还原被认为是缺氧含水层中一个重要的呼吸过程，但在分子水平上的研究还很有限。到目前为止，从铁还原生物到不溶性氧化铁相的电子转移被解释为三种类型的电子穿梭：矿物和细菌之间的直接接触，电子转移通过有机氧化还原活性电子穿梭，如醌，由微生物产生和分泌，最后腐殖酸作为氧化还原活性电子穿梭类似于醌。在目前的项目中，我们想研究一种新的机制，电子穿梭铁胶体。铁胶体通常存在于含水层中，其中铁还原被认为是主要的呼吸过程。与固体铁矿物如水铁矿相比，它们具有高活性。将研究胶体是否可以作为铁还原微生物的电子受体，以及它们是否可以将电子进一步穿梭到水铁矿。此外，我们将研究微生物还原过程是否会导致新铁胶体的产生，这将使电子穿梭通过胶体的自我维持的过程中，生物体不必投入能源生产的穿梭化合物。胶体方面的工作将得到实验的支持，通过测量生物体的生物量生长产量和产生的热量作为热力学能量增益的手段，确定固体氧化铁的氧化还原电位。

Microbial iron reduction is supposed to be an important respiration process in anoxic aquifers although only poorly investigated in molecular details. Until now, electron transfer from iron-reducing organisms to insoluble ferric oxide phases was explained by three types of electron shuttling: a direct contact between minerals and bacteria, electron transfer via organic redox active electron shuttles such as quinones which are produced and excreted by the microorganisms, and at last humic acids as redox active electron shuttles similar to quinones. In the current project we want to investigate a novel mechanism of electron shuttling by iron colloids. Iron colloids are often found in aquifers where iron reduction is supposed to be a major respiration process. They are highly reactive as compared to solid iron minerals such as ferrihydrite. It will be studied if colloids can serve as an electron acceptor for iron-reducing microorganisms and if they can shuttle the electrons further to ferrihydrite. Furthermore, we will investigate if the microbial reduction process leads to the generation of new iron colloids which would make the electron shuttling via colloids a self-sustaining process where the organisms do not have to invest energy in the production of the shuttle compound. The work on colloids will be supported by experiments to determine the redox potential of solid iron oxides by measuring the biomass growth yield of the organisms and the generated heat as a means for the thermodynamic energy gain.