The potential biogeochemical redox activity of arsenic was investigated by examining bacterial arsenic (As) redox genes such as cox, ars, and arr in arsenic-contaminated abandoned mine area and adjacent coastal sediments. Consistent with aerobic sediment and water samples from the mine through coastal areas, bacterial genes involing arsenic(V) (arsenate. AsO(4)(3-)) reduction such as arsC and arrA were identified only in a few samples, wheres bacterial aoxB gene encoding arsenite oxidase which is a central role in arsenic(III) (AsO(2)(-)) oxidation of aox operon. This study suggests that evaluation of arsenite-oxidizing bacteria including aox genotype may lead to a better understanding of molecular geomicrobiology in arsenic biogeochemistry, which can be applied to the bioremediation of arsenic contaminated mines along the coast of Gwangyang Bay. In this study, high concentrations of arsenic were observed in the mines and Gwangyang Bay and it was speculated that As(III)-oxidizing bacteria isolated from those highly arsenic-contaminated areas contributed the biogeochemical cycling of arsenic by transforming arsenic species and resulting in change of mobility, though further in situ biogeochemical and/or microbial ecological investigations are needed for confirming the phenomena in natural environment. Acinetobacter junni and Marinobacter sp. which were isolated in the contaminated area contained the aox genes and were able to oxidize As(III) to As(V), which is a more soluble form in oxic aqueous environments and apt to migrate from the mine to the coast. This might suggest a potential of a significant redox role of aox genes of arsenic-oxidizing bacteria in biogeochemical cycle of arsenic. (C) 2011 Elsevier B.V. All rights reserved.