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Appl. Environ. Microbiol. doi:10.1128/AEM.00840-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Anaerobic respiration of cobalt by Shewanella oneidensis strain MR-1: mechanism and consequences

BioTechnology Institute, Departments of Microbiology, and Chemical Engineering, University of Minnesota-Twin Cities, St. Paul MN 55108

^* To whom correspondence should be addressed. Email: gralnick{at}umn.edu.

	Abstract

Bacteria from the genus Shewanella are the most diverse respiratory organisms studied to date, and can utilize a variety of metals and metal(oids) as terminal electron acceptors. These bacteria can potentially be used in bioremediation applications since the redox state of metals often influences both solubility and toxicity. Understanding molecular mechanisms by which metal transformations occur and consequences of byproducts that may be toxic to the organism and thus inhibitory to the overall process is significant to future applications for bioremediation. Here, we examine the ability of Shewanella oneidensis to catalyze the reduction of chelated cobalt. We describe an unexpected ramification of Co(III)EDTA^- reduction by S. oneidensis: the formation of a toxic byproduct. We found that Co(II)EDTA^2-, the product of Co(III)EDTA^- respiration, inhibited growth of S. oneidensis strain MR-1 and that this toxicity is partially reversed by the addition of MgSO₄. We demonstrate that Co(III)EDTA^- reduction by S. oneidensis requires the Mtr extracellular respiratory pathway and associated pathways required to develop functional Mtr enzymes (c-type cytochrome maturation) and proper localization (type II secretion). The Mtr pathway is known to be required for a variety of substrates, including some chelated and insoluble metals and organic compounds. Understanding the full substrate range for the Mtr pathway is crucial for developing S. oneidensis as a tool for bioremediation.