The aim of this study was to characterize a facultative chemolithotrophic arsenite-oxidizing bacterium by evaluating the growth and the rate of arsenite oxidation and to investigate the genetic determinants for arsenic resistance and CO(2) fixation. The strain under study, Ancylobacter dichloromethanicus As3-1b, in a minimal medium containing 3 mM of arsenite as electron donor and 6 mM of CO(2)-bicarbonate as the C source, has a doubling time (t(d)) of 8.1 h. Growth and arsenite oxidation were significantly enhanced by the presence of 0.01 % yeast extract, decreasing the t(d) to 4.3 h. The strain carried arsenite oxidase (aioA) gene highly similar to those of previously reported arsenite-oxidizing Alpha-proteobacteria. The RuBisCO Type-I (cbbL) gene was amplified and sequenced too, underscoring the ability of As3-1b to carry out autotrophic As(III) oxidation. The results suggest that A. dichloromethanicus As3-1b can be a good candidate for the oxidation of arsenite in polluted waters or groundwaters.