Bacterial Oxidation of Arsenite II. The Activity of Washed Suspensions

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Abstract
Maximum arsenite-oxidizing activity of a pseudomonad (Pseudomonas arsenoxydans-quinque) isolated from "oxidized" arsenical cattle-dipping fluids was found in cells 3-4 days old, when cultivated in a synthetic medium containing arsenite. The system is adaptive since cells cultivated in the absence of arsenite show no arsenite-oxidizing activity. The oxidizing system in cells harvested at peak activity is optimally active in air at pH 6.4 and 40[degree]C, when tested in several different buffers. It is inhibited by cyanide and azide. Light-sensitive CO inhibition was demonstrated 6 months after the strain was 1st isolated, but 22 months later, after much sub-culturing, this property had been virtually lost. Inhibition was also observed with fluoride and pyrophosphate. Certain dicarbox-ylic acids produce a temporary inhibition between pH 4 and 5. Iodoacetate, auethyldithiocarbamate, alpha, alpha''-dipyridyl, and urethane have no effect. Cells are unable to oxidize arsenite in the presence of air after treatment with toluene, acetone, or after being subjected to desiccation. Since adapted cells can oxidize arsenite anaerobically in the presence of suitable acceptors, it is concluded that the complete system includes an arsenite dehydrogenase and cytochromes.