Humic Substances as a Mediator for Microbially Catalyzed Metal Reduction

• Published in: Acta Hydrochimica et Hydrobiologica 1998-05, Vol.26 (3), p.152-157
• Main Authors: Lovley, D. R., Fraga, J. L., Blunt-Harris, E. L., Hayes, L. A., Phillips, E. J. P., Coates, J. D.
• Format: Article
• Language: English
• Subjects: anaerob; Anaerobic; Biodegradation of pollutants; Biological and medical sciences; biologische Sanierung; Bioremediation; Biotechnology; Chinone; Eisenoxide; Environment and pollution; Fundamental and applied biological sciences. Psychology; Humic Substances; Huminstoffe; Industrial applications and implications. Economical aspects; Iron Oxides; Quinones
• ISSN: 0323-4320; 1521-401X
• DOI: 10.1002/(SICI)1521-401X(199805)26:3<152::AID-AHEH152>3.0.CO;2-D

The potential for humic substances to serve as a terminal electron acceptor in microbial respiration and to function as an electron shuttle between Fe(III)‐reducing microorganisms and insoluble Fe(III) oxides was investigated. The Fe(III)‐reducing microorganism Geobacter metallireducens conserved energy to support growth from electron transport to humics as evidenced by continued oxidation of acetate to carbon dioxide after as many as nine transfers in a medium with acetate as the electron donor and soil humic acids as the electron acceptor. Growth of G. metallireducens with poorly crystalline Fe(III) oxide as the electron acceptor was greatly stimulated by the addition of as little as 100 μM of the humics analog, anthraquinone‐2,6‐disulfonate. Other quinones investigated, including lawsone, menadione, and anthraquinone‐2‐sulfonate, also stimulated Fe(III) oxide reduction. A wide phylogenetic diversity of microorganisms capable of Fe(III) reduction were also able to transfer electrons to humics. Microorganisms which can not reduce Fe(III) could not reduce humics. Humics stimulated the reduction of structural Fe(III) in clay and the crystalline Fe(III) forms, goethite and hematite. These results demonstrate that electron shuttling between Fe(III)‐reducing microorganisms and Fe(III) via humics not only accelerates the microbial reduction of poorly crystalline Fe(III) oxide, but also can facilitate the reduction of Fe(III) forms that are not typically reduced by microorganisms in the absence of humics. Addition of humic substances to enhance electron shuttling between Fe(III)‐reducing microorganisms and Fe(III) oxides may be a useful strategy to stimulate the remediation of soils and sediments contaminated with organic or metal pollutants. Huminstoffe als Vermittler bei der mikrobiell katalysierten Metallreduktion Es wurde untersucht, inwieweit Huminstoffe als terminale Elektronenakzeptoren bei der mikrobiellen Atmung und als Vermittler bei der Elektronenübertragung zwischen Fe(III)‐reduzierenden Mikroorganismen und unlöslichen Fe(III)‐oxiden fungieren können. Das Fe(III)‐reduzierende Bakterium Geobacter metallireducens gewinnt Energie zum Wachstum aus der Elektronenübertragung auf Huminstoffe. Das wurde offensichtlich, als nach 9 aufeinanderfolgenden Transfers des Bakteriums auf frisches Medium mit Acetat als Elektronendonor und Boden‐Huminstoff als Elektronenakzeptor seine Fähigkeit zur Oxidation von Acetat zu CO2 erhalten blieb. Das Wachstum von G. metalli