Redox activity of humic substances and their role as electron shuttles between microorganisms and Fe(III)-minerals

• Applicant: Professor Dr. Andreas Kappler
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
• Term: from 2006 to 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5471696

Humified natural organic matter (humic substances) is present in most aquatic and terrestrial environments; it is redox-active, can be reduced chemically and microbially and interacts with organic and inorganic contaminants by adsorption, complexation and redox reactions. In the first funding period of this research project we demonstrated that humic substances can function as electron shuttles in anoxic aquifers. However, the specific conditions under which this shuttling can happen and the molecular processes involved in humic substance electron shuttling are still unknown. In this follow-up project we therefore intend to identify whether humic substances can function as electron shuttle between microbes and solid-phase electron acceptors under conditions as they could be present in anoxic aquifers with regard to the concentrations of humic substances, presence of silica and other ions (e.g. phosphate), different ratios of iron minerals to microbial cells, spatial distances between cells and iron minerals as well as identity and quantity of iron minerals. This interdisciplinary research project combines microbiological, geochemical, mineralogical, spectroscopical and modeling studies to better understand the role of humic substances in microbial and chemical redox processes in anoxic environments.

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