Abstract
A bacterial strain B2 that oxidizes arsenite into arsenate was isolated from the biofilm growing in a biological groundwater treatment process used for Fe removal. This strain is phylogenetically and morphologically different from the genus Leptothrix commonly encountered in biological iron oxidation processes. T-RFLP fingerprint of the biofilm revealed that this isolated strain B2 corresponds to the major population of the bacterial community in the biofilm. Therefore, it is probably one of the major contributors to arsenic removal in the treatment process.