DECREASED PERMEABILITY AS THE MECHANISM OF ARSENITE RESISTANCE IN PSEUDOMONAS PSEUDOMALLEI

Abstract

The mechanism of arsenite resistance of Pseudomonas pseudomallei strain-54, isolated from soil, was studied by use of radioactive arsenite. Arsenite resistance was found to be related to decreased permeation of arsenite into the cells. P. pseudomallei-54 cells can accumulate arsenite, but the organisms grown adaptively in the presence of arsenite accumulate only a small amount of the drug. Arsenite accumulated in the cells can exchange freely with extracellular arsenite. The apparent dissociation constant of the "bacterium-arsenite complex" was calculated as 5.9 x 10"5 [image] for the sensitive cells and 6.3 x 10-4 [image] for the resistant ones. No significant difference was observed in the arsenite capacity (maximal uptake) of the cells (2 x 10-3 mmoles per 30 mg of dry cells). The uptake of arsenite by the sensitive cells was markedly dependent on temperature, but it was not inhibited by 2,4-dinitrophenol (5 x 10-3 [image]) and sodium-azide (10-2 [image]). Omission of the substrate, a-ketoglutarate, from the incubation mixture had no inhibitory effect on arsenite uptake. Treatment of the resistant cells with cetyl-trimethylammonium-bromide facilitated the uptake of arsenite by the cells. When the sensitive cells accumulating radioactive arsenite were fractionated by the Schmidt-Thanhauser-Schneider method, the large amount of intra-cellular arsenite was found in the cold perchloric acid-insoluble hot acid-extractable fraction. The arsenite complex with cellular macromolecular constituents cannot be solubilized by treatment with ribonuclease, deoxyribonuclease and trypsin.