title: The cymA gene, encoding a tetraheme c-type cytochrome, is required for arsenate respiration in Shewanella species.
abstract: In Shewanella sp. strain 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 putrefaciens strain CN-32 showed that it also contained the same arrAB operon with 100% nucleotide identity. 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 on and reduction of arsenate. The DeltacymA strains of CN-32 and ANA-3 negatively affected the reduction of Fe(III) and Mn(IV) but not growth on nitrate. Unlike the CN-32 DeltacymA strain, growth on fumarate was absent in the DeltacymA strain of ANA-3. Both homologous and heterologous complementation of cymA in trans restored growth on arsenate in DeltacymA strains of both 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 in 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 species Shewanella oneidensis strain MR-1, has pleiotropic effects on Fe(III), Mn(IV), dimethyl sulfoxide, nitrate, nitrite, and fumarate respiration.
authors.affiliation: Department of Environmental Toxicology, University of California, Santa Cruz, Santa Cruz, CA 95064, USA.
authors.forename: Julie N
authors.initials: JN
authors.lastname: Murphy
authors.forename: Chad W
authors.initials: CW
authors.lastname: Saltikov
mesh_terms: D000595:Amino Acid Sequence; D053502:Arsenate Reductases / Q000235:genetics / Q000378:metabolism*; D001149:Arsenates / Q000378:metabolism*; D003470:Culture Media; D003574:Cytochrome c Group / Q000235:genetics* / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D007506:Iron-Sulfur Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D008982:Molybdenum / Q000378:metabolism; D009154:Mutation; D010084:Oxidation-Reduction; D020592:Shewanella / Q000145:classification* / Q000201:enzymology / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D020614:Shewanella putrefaciens / Q000201:enzymology / Q000235:genetics / Q000502:physiology
chemical_list: D001149:Arsenates; D003470:Culture Media; D003574:Cytochrome c Group; D007506:Iron-Sulfur Proteins; D008982:Molybdenum; C017165:cytochrome c(3); D053502:Arsenate Reductases; C025657:arsenic acid