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Applied and Environmental Microbiology, January 2006, p. 686-694, Vol. 72, No. 1
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.1.686-694.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Anaerobic Nitrate-Dependent Iron(II) Bio-Oxidation by a Novel Lithoautotrophic Betaproteobacterium, Strain 2002

Karrie A. Weber,1 Jarrod Pollock,2,{dagger} Kimberly A. Cole,2,{ddagger} Susan M. O'Connor,1 Laurie A. Achenbach,2 and John D. Coates1*

University of California, Department of Plant and Microbial Biology, Berkeley, California 94720-3102,1 Southern Illinois University, Department of Microbiology, Carbondale, Illinois 629012

Received 13 July 2005/ Accepted 13 October 2005

Microbial nitrate-dependent Fe(II) oxidation is known to contribute to iron biogeochemical cycling; however, the microorganisms responsible are virtually unknown. In an effort to elucidate this microbial metabolic process in the context of an environmental system, a 14-cm sediment core was collected from a freshwater lake and geochemically characterized concurrently with the enumeration of the nitrate-dependent Fe(II)-oxidizing microbial community and subsequent isolation of a nitrate-dependent Fe(II)-oxidizing microorganism. Throughout the sediment core, ambient concentrations of Fe(II) and nitrate were observed to coexist. Concomitant most probable number enumeration revealed the presence of an abundant nitrate-dependent Fe(II)-oxidizing microbial community (2.4 x 103 to 1.5 x 104 cells g–1 wet sediment) from which a novel anaerobic, lithoautotrophic, Fe(II)-oxidizing bacterium, strain 2002, was isolated. Analysis of the complete 16S rRNA gene sequence revealed that strain 2002 was a member of the beta subclass of the proteobacteria with 94.8% similarity to Chromobacterium violaceum, a bacterium not previously recognized for the ability to oxidize nitrate-dependent Fe(II). Under nongrowth conditions, both strain 2002 and C. violaceum incompletely reduced nitrate to nitrite with Fe(II) as the electron donor, while under growth conditions nitrate was reduced to gaseous end products (N2 and N2O). Lithoautotrophic metabolism under nitrate-dependent Fe(II)-oxidizing conditions was verified by the requirement of CO2 for growth as well as the assimilation of 14C-labeled CO2 into biomass. The isolation of strain 2002 represents the first example of an anaerobic, mesophilic, neutrophilic Fe(II)-oxidizing lithoautotroph isolated from freshwater samples. Our studies further demonstrate the abundance of nitrate-dependent Fe(II) oxidizers in freshwater lake sediments and provide further evidence for the potential of microbially mediated Fe(II) oxidation in anoxic environments.

* Corresponding author. Mailing address: University of California, Department of Plant and Microbial Biology, 271 Koshland Hall, Berkeley, CA. Phone: (510) 643-8455. Fax: (510) 642-4995. E-mail: jcoates{at}nature.berkeley.edu

{dagger} Present address: University of Montana, Division of Biological Sciences, Missoula, MT 59812-4824.

{ddagger} Present address: BioInsite LLC, 150 E. Pleasant Hill Rd., Suite 173, Carbondale, IL 62901.

Applied and Environmental Microbiology, January 2006, p. 686-694, Vol. 72, No. 1
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.1.686-694.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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