Microbial oxidation of arsenite and occurrence of arsenite‐oxidizing bacteria in acid mine water from a sulfur‐pyrite mine

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Abstract
The acid mine waters (pH 2.0-2.4) discharged from the Matsuo sulfur-pyrite mine contained high concentrations of dissolved inorganic arsenic (2-13 ppm). Arsenic in the superficial acid mine waters was predominantly in the (V) state (arsenate); however, the element in the water from a deep mine drift was almost in the (III) state (arsenite). Microbial arsenite oxidation occurred in the acid mine waters and along the stream of the river, which was contaminated with a large volume of the mine drift water. Arsenite (500 ppm As)-resistant bacteria (0-27 colonies/ml) were detected in the water samples and 208 slant cultures were obtained. Arsenite-oxidizing activities of all the cultures were determined and six strains with strong arsenite-oxidizing activity were isolated. These bacteria were acidophilic (optimum growth pH, 3-4), gram-negative, aerobic, and rod-shaped. They could not oxidize ferrous iron and elemental sulfur as a sole energy source and not derive the energy for chemoautotrophic growth from arsenite oxidation.