DECREASED PERMEABILITY AS THE MECHANISM OF ARSENITE RESISTANCE IN PSEUDOMONAS PSEUDOMALLEI.

Beppu, Michiko (University of Tokyo, Tokyo, Japan), and Kei Arima. Decreased permeability as the mechanism of arsenite resistance in Pseudomonas pseudomallei. J. Bacteriol. 88:151-157. 1964.-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)m for the sensitive cells and 6.3 x 10(-4)m 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)m) and sodium azide (10(-2)m). Omission of the substrate, alpha-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 intracellular 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.