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J. Bacteriol. doi:10.1128/JB.01698-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The cymA gene encoding a tetraheme c-type cytochrome is required for arsenate respiration in Shewanella species

University of California, Santa Cruz, Dept. Environmental Toxicology, Santa Cruz, CA 95064

^* To whom correspondence should be addressed. Email: saltikov{at}etox.ucsc.edu.

	Abstract

In Shewanella sp. ANA-3, utilization of arsenate as a terminal electron acceptor is conferred by a two-gene operon, arrAB, which lacks a gene encoding a membrane anchoring subunit for the soluble ArrAB protein complex. Analysis of the genome sequence of Shewanella putrefacians strain CN-32 showed it also contained the same arrAB operon with 100% nucleotide identities. Here we report that CN-32 respires arsenate and that this metabolism is dependent on arrA and an additional gene encoding a membrane associated tetraheme c-type cytochrome, cymA. Deletion of cymA in ANA-3 also eliminated growth and reduction of arsenate. The cymA strains of CN-32 and ANA-3 negatively affected reduction of Fe(III) and Mn(IV) but not growth on nitrate. Unlike CN-32 cymA strain, growth on fumarate was absent in the cymA strain of ANA-3. Both homologous and heterologous complementation of cymA in trans restored growth on arsenate in both cymA strains of CN-32 and ANA-3. Transcription patterns of cymA showed that it was induced under anaerobic conditions in the presence of fumarate and arsenate. Nitrate-grown cells exhibited the greatest level of cymA expression in both wild-type strains. Lastly, site directed mutagenesis of the first Cys to Ser of each of the four CXXCH c-heme binding motifs of the CN-32 CymA nearly eliminated growth on and reduction of arsenate. Together, these results indicate that the biochemical mechanism of arsenate respiration and reduction requires the interactions of ArrAB with a membrane associated tetraheme cytochrome, which in the non-arsenate respiring Shewanella, S. oneidensis strain MR-1, has pleiotropic effects on Fe(III), Mn(IV), DMSO, nitrate, nitrite, and fumarate respiration.

This article has been cited by other articles:

• Malasarn, D., Keeffe, J. R., Newman, D. K. (2008). Characterization of the Arsenate Respiratory Reductase from Shewanella sp. Strain ANA-3. J. Bacteriol. 190: 135-142 [Abstract] [Full Text]