title: Arsenite oxidase also functions as an antimonite oxidase.
abstract: Arsenic and antimony are toxic metalloids and are considered priority environmental pollutants by the U.S. Environmental Protection Agency. Significant advances have been made in understanding microbe-arsenic interactions and how they influence arsenic redox speciation in the environment. However, even the most basic features of how and why a microorganism detects and reacts to antimony remain poorly understood. Previous work with Agrobacterium tumefaciens strain 5A concluded that oxidation of antimonite [Sb(III)] and arsenite [As(III)] required different biochemical pathways. Here, we show with in vivo experiments that a mutation in aioA [encoding the large subunit of As(III) oxidase] reduces the ability to oxidize Sb(III) by approximately one-third relative to the ability of the wild type. Further, in vitro studies with the purified As(III) oxidase from Rhizobium sp. strain NT-26 (AioA shares 94% amino acid sequence identity with AioA of A. tumefaciens) provide direct evidence of Sb(III) oxidation but also show a significantly decreased Vmax compared to that of As(III) oxidation. The aioBA genes encoding As(III) oxidase are induced by As(III) but not by Sb(III), whereas arsR gene expression is induced by both As(III) and Sb(III), suggesting that detection and transcriptional responses for As(III) and Sb(III) differ. While Sb(III) and As(III) are similar with respect to cellular extrusion (ArsB or Acr3) and interaction with ArsR, they differ in the regulatory mechanisms that control the expression of genes encoding the different Ars or Aio activities. In summary, this study documents an enzymatic basis for microbial Sb(III) oxidation, although additional Sb(III) oxidation activity also is apparent in this bacterium.
authors.affiliation: State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, People's Republic of China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Wang
authors.affiliation: Institute of Structural & Molecular Biology, University College London, London, United Kingdom.
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Warelow
authors.affiliation: Department of Land Resources & Environmental Sciences, Montana State University, Bozeman, Montana, USA.
authors.forename: Yoon-Suk
authors.initials: YS
authors.lastname: Kang
authors.affiliation: Department of Land Resources & Environmental Sciences, Montana State University, Bozeman, Montana, USA.
authors.forename: Christine
authors.initials: C
authors.lastname: Romano
authors.affiliation: Institute of Structural & Molecular Biology, University College London, London, United Kingdom.
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Osborne
authors.affiliation: Chemistry & Biochemistry Department, California Polytechnic State University, San Luis Obispo, California, USA.
authors.forename: Corinne R
authors.initials: CR
authors.lastname: Lehr
authors.affiliation: Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Bothner
authors.affiliation: Department of Land Resources & Environmental Sciences, Montana State University, Bozeman, Montana, USA.
authors.forename: Timothy R
authors.initials: TR
authors.lastname: McDermott
authors.affiliation: Institute of Structural & Molecular Biology, University College London, London, United Kingdom j.santini@ucl.ac.uk gejiao@mail.hzau.edu.cn.
authors.forename: Joanne M
authors.initials: JM
authors.lastname: Santini
authors.affiliation: State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, People's Republic of China j.santini@ucl.ac.uk gejiao@mail.hzau.edu.cn.
authors.forename: Gejiao
authors.initials: G
authors.lastname: Wang
mesh_terms: D016960:Agrobacterium tumefaciens / Q000201:enzymology* / Q000378:metabolism*; D000965:Antimony / Q000378:metabolism*; D018053:Arsenites / Q000378:metabolism*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism*; D012231:Rhizobium / Q000201:enzymology / Q000378:metabolism
chemical_list: D018053:Arsenites; C061374:antimonite; D000965:Antimony; D010088:Oxidoreductases; C078179:arsenite oxidase; C015001:arsenite