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Applied and Environmental Microbiology, June 2003, p. 3517-3525, Vol. 69, No. 6
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.6.3517-3525.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Chemical and Biological Interactions during Nitrate and Goethite Reduction by Shewanella putrefaciens 200

D. Craig Cooper,^1* Flynn W. Picardal,¹ Arndt Schimmelmann,² and Aaron J. Coby¹

Environmental Science Research Center, School of Public and Environmental Affairs,¹ Department of Geological Sciences, Indiana University, Bloomington, Indiana 47405-1405²

Received 15 August 2002/ Accepted 5 March 2003

Although previous research has demonstrated that NO₃^- inhibits microbial Fe(III) reduction in laboratory cultures and natural sediments, the mechanisms of this inhibition have not been fully studied in an environmentally relevant medium that utilizes solid-phase, iron oxide minerals as a Fe(III) source. To study the dynamics of Fe and NO₃^- biogeochemistry when ferric (hydr)oxides are used as the Fe(III) source, Shewanella putrefaciens 200 was incubated under anoxic conditions in a low-ionic-strength, artificial groundwater medium with various amounts of NO₃^- and synthetic, high-surface-area goethite. Results showed that the presence of NO₃^- inhibited microbial goethite reduction more severely than it inhibited microbial reduction of the aqueous or microcrystalline sources of Fe(III) used in other studies. More interestingly, the presence of goethite also resulted in a twofold decrease in the rate of NO₃^- reduction, a 10-fold decrease in the rate of NO₂^- reduction, and a 20-fold increase in the amounts of N₂O produced. Nitrogen stable isotope experiments that utilized ¹⁵N values of N₂O to distinguish between chemical and biological reduction of NO₂^- revealed that the N₂O produced during NO₂^- or NO₃^- reduction in the presence of goethite was primarily of abiotic origin. These results indicate that concomitant microbial Fe(III) and NO₃^- reduction produces NO₂^- and Fe(II), which then abiotically react to reduce NO₂^- to N₂O with the subsequent oxidation of Fe(II) to Fe(III).

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* Corresponding author. Present address: Geosciences Research, IF-IRC MS 2107, Idaho National Engineering and Environmental Laboratory, P.O. Box 1625, Idaho Falls, ID 83404-2107. Phone: (208) 526-5395. Fax: (208) 526-0875. E-mail: coopdc{at}inel.gov.

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Applied and Environmental Microbiology, June 2003, p. 3517-3525, Vol. 69, No. 6
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.6.3517-3525.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

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