title: A C⋅As lyase for degradation of environmental organoarsenical herbicides and animal husbandry growth promoters.
abstract: Arsenic is the most widespread environmental toxin. Substantial amounts of pentavalent organoarsenicals have been used as herbicides, such as monosodium methylarsonic acid (MSMA), and as growth enhancers for animal husbandry, such as roxarsone (4-hydroxy-3-nitrophenylarsonic acid) [Rox(V)]. These undergo environmental degradation to more toxic inorganic arsenite [As(III)]. We previously demonstrated a two-step pathway of degradation of MSMA to As(III) by microbial communities involving sequential reduction to methylarsonous acid [MAs(III)] by one bacterial species and demethylation from MAs(III) to As(III) by another. In this study, the gene responsible for MAs(III) demethylation was identified from an environmental MAs(III)-demethylating isolate, Bacillus sp. MD1. This gene, termed arsenic inducible gene (arsI), is in an arsenic resistance (ars) operon and encodes a nonheme iron-dependent dioxygenase with C ⋅ As lyase activity. Heterologous expression of ArsI conferred MAs(III)-demethylating activity and MAs(III) resistance to an arsenic-hypersensitive strain of Escherichia coli, demonstrating that MAs(III) demethylation is a detoxification process. Purified ArsI catalyzes Fe(2+)-dependent MAs(III) demethylation. In addition, ArsI cleaves the C ⋅ As bond in trivalent roxarsone and other aromatic arsenicals. ArsI homologs are widely distributed in prokaryotes, and we propose that ArsI-catalyzed organoarsenical degradation has a significant impact on the arsenic biogeocycle. To our knowledge, this is the first report of a molecular mechanism for organoarsenic degradation by a C ⋅ As lyase.
authors.affiliation: Department of Cellular Biology and Pharmacology, Herbert Wertheim College of Medicine, Florida International University, Miami, FL 33199 myoshina@fiu.edu.
authors.forename: Masafumi
authors.initials: M
authors.lastname: Yoshinaga
authors.affiliation: Department of Cellular Biology and Pharmacology, Herbert Wertheim College of Medicine, Florida International University, Miami, FL 33199.
authors.forename: Barry P
authors.initials: BP
authors.lastname: Rosen
mesh_terms: D000595:Amino Acid Sequence; D001152:Arsenicals / Q000378:metabolism*; D001407:Bacillus / Q000201:enzymology* / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology*; D001483:Base Sequence; D001673:Biodegradation, Environmental / Q000187:drug effects; D016000:Cluster Analysis; D049308:Dioxygenases / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology*; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli; D006540:Herbicides / Q000378:metabolism*; D008190:Lyases / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012406:Roxarsone / Q000378:metabolism*; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D014461:Ultracentrifugation
chemical_list: D001152:Arsenicals; D001426:Bacterial Proteins; D006540:Herbicides; D012336:RNA, Ribosomal, 16S; D049308:Dioxygenases; D008190:Lyases; D012406:Roxarsone; C020300:monomethylarsonic acid
keywords: growth promoter degradation; herbicide resistance