Interaction of Arsenate with Phosphate-Transport Systems in Wild-Type and Mutant Streptococcus faecalis

Abstract

Harold , F. M. (National Jewish Hospital, Denver, Colo.), and J. R. Baarda . Interaction of arsenate with phosphate-transport systems in wild-type and mutant Streptococcus faecalis . J. Bacteriol. 91: 2257–2262. 1966.—Arsenate competitively inhibits the growth of Streptococcus faecalis , primarily by competition with phosphate for a common transport system. Arsenate is itself accumulated by the cells; the uptake requires metabolic energy, and the intracellular arsenate level may reach 0.01 m . Cells loaded with arsenate have lost the capacity to take up radioactive glutamate, rubidium, phosphate, or arsenate itself, apparently by the uncoupling of adenosine triphosphate generation. The p H dependence of arsenate uptake is complex. At low concentrations of extracellular arsenate, uptake by the wild-type strain 9790 exhibits a single maximum about p H 8; mutant PT-1, previously shown to be defective in phosphate uptake, takes up essentially no arsenate. At high concentrations of arsenate, uptake by the wild type is bimodal with maxima at p H 5.5 and 9; the uptake curve for mutant PT-1 corresponds to the shoulder in the curve for the wild type. The apparent dissociation constant for arsenate uptake by the wild type is approximately 10 −5 m from p H 5 to 9, whereas that for mutant PT-1 is about 5 × 10 −5 M at p H 5 and rises rapidly with increasing p H. The results confirm the earlier conclusion that the lesion in mutant PT-1 resides in the transport of phosphate and arsenate. It is proposed that the wild type has two distinct transport systems, whereas the mutant has lost the one with alkaline p H optimum.