Microorganisms play an important role in many surface and near-surface geochemical environments. Partial physicochemical characterization of Xichu River waters showed high concentrations of As (98 μg L–1) in the zone of the “Aurora” mine probably due to arsenic release into the environment through metal sulfide oxidation. Several microorganisms strains resistant or tolerant to 20mM of As(III) or As(V) were isolated from the river water, sediments and/or biofilms. The microorganisms likely interact with arsenic through mechanisms such as sorption, mobilization, precipitation and redox reactions, understanding of which may facilitate the development of new bio-treatments.