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Letters to Nature
Nature 382, 445 - 448 (01 August 1996); doi:10.1038/382445a0

Humic substances as electron acceptors for microbial respiration

Derek R. Lovley*, John D. Coates, Elizabeth L. Blunt-Harris*, Elizabeth J. P. Phillips & Joan C. Woodward*

*Department of Microbiology, University of Massachusetts, Amherst, Massachusetts 01003, USA
Water Resources Division, US Geological Survey, Reston, Virginia 22092, USA

HUMIC substances are heterogeneous high-molecular-weight organic materials which are ubiquitous in terrestrial and aquatic environments. They are resistant to microbial degradation1 and thus are not generally considered to be dynamically involved in microbial metabolism, especially in anoxic habitats. However, we show here that some microorganisms found in soils and sediments are able to use humic substances as an electron acceptor for the anaerobic oxidation of organic compounds and hydrogen. This electron transport yields energy to support growth. Microbial humic reduction also enhances the capacity for microorganisms to reduce other, less accessible electron acceptors, such as insoluble Fe(III) oxides, because humic substances can shuttle electrons between the humic-reducing microorganisms and the Fe(III) oxide. The finding that microorganisms can donate electrons to humic acids has important implications for the mechanisms by which microorganisms oxidize both natural and contaminant organics in anaerobic soils and sediments, and suggests a biological source of electrons for humics-mediated reduction of contaminant metals and organics.



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