Six novel bacterial strains were isolated from the environment which can oxidize arsenite [As(III)] to the less mobile form arsenate [As(V)] coupled to CO2 fixation under either aerobic or denitrifying conditions. PCR primers were designed to the conserved molybdopterin domain of the large subunit of arsenite oxidase in order to identify the arsenite oxidase genes from these isolates. The amino acid sequences for the arsenite oxidases reported here were 72-74% identical to that of strain NT-26, the only previously reported autotrophic arsenite oxidizer. Indeed the autotrophic arsenite oxidase genes form a distinct phylogenetic group, separated from previously described heterotrophic arsenite oxidase genes, with the exception of the heterotroph Agrobacterium tumefaciens. The arsenite oxidase primers described here represent a powerful culture-independent tool to assess the diversity of arsenite oxidase genes in environmental bacteria. (c) 2007 Elsevier Inc. All rights reserved.