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Applied and Environmental Microbiology, September 2003, p. 5255-5262, Vol. 69, No. 9
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.9.5255-5262.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Nitrilotriacetate Stimulation of Anaerobic Fe(III) Respiration by Mobilization of Humic Materials in Soil

Y. Luu, B. A. Ramsay, and J. A. Ramsay*

Department of Chemical Engineering, Queen's University, Kingston, Ontario K7L 3N6, Canada

Received 15 April 2003/ Accepted 24 June 2003

An enrichment culture capable of naphthalene mineralization reduced Fe(III) oxides without direct contact in anaerobic soil microcosms when the Fe(III) was placed in dialysis membranes or entrapped within alginate beads. Both techniques demonstrated that a component in soil, possibly humic materials, facilitated Fe(III) reduction when direct contact between cells and Fe(III) was not possible. The addition of the synthetic Fe(III) chelator, nitrilotriacetic acid (NTA), to soil enhanced Fe(III) reduction across the dialysis membrane and alginate beads, with the medium changing from clear to a dark brown color. An NTA-soil extract was more effective in Fe(III) reduction than the extracted soil itself. Characteristics of the NTA extract were consistent with that of humic substances. The results indicate that NTA improved Fe(III) reduction not by Fe(III) solubilization but by extraction of humic substances from soil into the aqueous medium. This is the first study in which stimulation of Fe(III) reduction through the addition of chemical chelators is shown to be due to the extraction of electron-shuttling compounds from the soil and not to solubilization of the Fe(III) and indicates that mobilization of humic materials could be an important component of anaerobic biostimulation.

* Corresponding author. Mailing address: Department of Chemical Engineering, Queen's University, Kingston, Ontario, Canada K7L 3N6. Phone: (613) 533-2770. Fax: (613) 533-6637. E-mail: ramsayj{at}chee.queensu.ca.

Applied and Environmental Microbiology, September 2003, p. 5255-5262, Vol. 69, No. 9
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.9.5255-5262.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.





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