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J. Biol. Chem., Vol. 280, Issue 24, 22590-22595, June 17, 2005

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ChrR, a Soluble Quinone Reductase of Pseudomonas putida That Defends against H₂O₂^*

Claudio F. Gonzalez, David F. Ackerley¶, Susan V. Lynch, and A. Matin||

From the Department of Microbiology and Immunology, Sherman Fairchild Science Building, Stanford University School of Medicine, Stanford, California 94305

Most bacteria contain soluble quinone-reducing flavoenzymes. However, no biological benefit for this activity has previously been demonstrated. ChrR of Pseudomonas putida is one such enzyme that has also been characterized as a chromate reductase; yet we propose that it is the quinone-reducing activity of ChrR that has the greatest biological significance. ChrR reduces quinones by simultaneous two-electron transfer, avoiding formation of highly reactive semiquinone intermediates and producing quinols that promote tolerance of H₂O₂. Expression of chrR was induced by H₂O₂, and levels of chrR expression in overexpressing, wild type, and knock-out mutant strains correlated with the H₂O₂ tolerance and scavenging ability of each strain. The chrR expression level also correlated with intracellular H₂O₂ levels as measured by protein carbonylation assays and fluorescence-activated cell scanning analysis with the H₂O₂-responsive dye H₂DCFDA. Thus, enhancing the activity of ChrR in a chromate-remediating bacterial strain may not only increase the rate of chromate transformation, it may also augment the capacity of these cells to withstand the unavoidable production of H₂O₂ that accompanies chromate reduction.

Received for publication, February 11, 2005 , and in revised form, April 11, 2005.

^* This work was supported by Grants DE-FG02-03ER63627 and NAG2-1 (to A. M.) from the Natural and Accelerated Bioremediation Program, Biological and Environmental Research, United States Department of Energy and NASA, respectively. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

These authors contributed equally to this work and should be regarded as joint first authors.

Supported by a postdoctoral fellowship from Conicet, Argentina.

^¶ Supported by a postdoctoral fellowship STAX0101 from Foundation for Research, Science, and Technology, New Zealand.

^|| To whom correspondence should be addressed. Tel.: 650-725-4745; Fax: 650-725-6757; E-mail: a.matin{at}stanford.edu.

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