Effects of humic substances and quinones at low concentrations on ferrihydrite reduction by Geobacter metallireducens

Manfred Wolf, Andreas Kappler, Jie Jiang, Rainer U. Meckenstock

Research output: Contribution to journalArticlepeer-review

182 Scopus citations

Abstract

Humic substances (HS) and quinones can accelerate dissimilatory Fe(III) reduction by electron shuttling between microorganisms and poorly soluble iron(III) (hydr)oxides. The mechanism of electron shuttling for HS is not fully understood, but it is suggested that the most important redox-active components in HS are also quinones. Here we studied the influence of HS and different quinones at low concentrations on ferrihydrite reduction by Geobacter metallireducens. The aquatic HS used were humic and fulvic acids (HA and FA) isolated from groundwater of a deep aquifer in Gorleben (Niedersachsen, Germany).HAstimulated iron reduction stronger than FA down to total HA concentrations as low as 1 mg/L. The quinones studied showed large differences:somehad strong accelerating effects, whereas others showed only small effects, no effects, or even inhibitory effects on the kinetics of iron reduction. We found that the redox potentials of the most active quinones fall in a narrow range of -137 to -225 mV vs NHE at pH 7. These results give evidence that the kinetic of microbial iron reduction mediated by electron shuttles is mainly controlled by thermodynamic parameters, i.e., by the redox potential of the shuttle compound, rather than by the proportion of dissolved vs adsorbed compound.

Original languageEnglish
Pages (from-to)5679-5685
Number of pages7
JournalEnvironmental Science and Technology
Volume43
Issue number15
DOIs
StatePublished - 1 Aug 2009
Externally publishedYes

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