A novel mechanism of electron transfer from microorganisms to insoluble iron phases
FOR 580 MEC
Von 02/2006Projektleiter: Rainer U. Meckenstock
Bewilligung: FOR 580 Electron Transfer Processes in Anoxic Aquifers
Microbial iron reduction is supposed to be an important respiration process in anoxic aquifers although only poorly understood 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 humic acids as redox active electron shuttles similar to quinones. In the current project we describe a novel mechanism of electron shuttling by iron oxide colloids. Iron oxide nano-particles are often found in aquifers where iron reduction is supposed to be a major respiration process. In the first funding period we could show that ferric iron colloids are reduced up to 300-fold faster reduced by microorganisms as compared to solid iron minerals such as ferrihydrite. Furthermore, nano-particles of goethite and hematite can be readily reduced by microbes although they are not reducible as a bulk phase. It will be studied here under which environmental conditions colloids can serve as an electron acceptor for iron-reducing microorganisms and if they can shuttle the electrons further to ferrihydrite. This will be complemented by studies on how the catalytic electron shuttling between the microbial cells and the bulk ferric oxide is catalysed on a molecular and mineralogical level.