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

• Applicant: Professor Dr. Rainer Udo Meckenstock
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
• Term: from 2006 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5471696

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.

• DFG Programme: Research Units
• Subproject of: FOR 580: Electron Transfer Processes in Anoxic Aquifers