A C⋅As lyase for degradation of environmental organoarsenical herbicides and animal husbandry growth promoters

Significance Organoarsenicals are used as herbicides, pesticides, antimicrobial growth promoters, and chemical warfare agents. Environmental organoarsenicals are microbially degraded, but the molecular mechanisms of breakdown are unknown. We previously identified a two-step pathway of degradation involving sequential reduction and C⋅As bond cleavage. Here we report cloning of the gene and characterization of the gene product for a C⋅As lyase, ArsI, a member of the family of type I extradiol dioxygenases. ArsI is the only enzyme shown to be involved in degradation of the reduced forms of the herbicide monosodium methylarsonic acid and the antimicrobial growth promoter roxarsone. AsarsI genes are widely distributed in bacteria, ArsI-catalyzed organoarsenic degradation is proposed to have an impact on the arsenic biogeocycle.