Summary ......................................................... 3
Zusammenfassung ................................................. 5
1 Humic substances and extracellular electron transfer ......... 9
Objectives of the thesis .................................... 35
2 Structural iron in humic acids and its contribution to
humic acid redox activity ................................... 37
3 Humics as fully regenerable terminal electron acceptors in
recurrently anoxic environments ............................. 49
4 Outer-membrane cytochrome-independent reduction of
extracellular electron acceptors in Shewanella oneidensis ... 87
5 Dependence of microbial magnetite formation on humic
substance and ferrihydrite concentrations .................. 125
6 Electron transfer from humic substances to biogenic and
abiogenic Fe(III) oxyhydroxide minerals .................... 155
7 Electron shuttling by dissolved and solid-phase organic
matter present in a riparian aquifer sediment .............. 177
8 Humic substance- and Fe(III)-reducing microorganisms
and the imriortance of electron shuttling in anoxic
aquifers ................................................... 191
Discussion and Outlook ........................................ 221
Statement of Personal Contribution ............................ 235
Acknowledgements .............................................. 237
Curriculum Vitae .............................................. 239
List of Publications .......................................... 240
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