Effect of arsenate on inorganic phosphate transport in Escherichia coli

The effect of arsenate on strains dependent on the two major inorganic phosphate (P(i)) transport systems in Escherichia coli was examined in cells grown in 1 mM phosphate medium. The development of arsenate-resistant P(i) uptake in a strain dependent upon the Pst (phosphate specific transport) system was examined. The growth rate of Pst-dependent cells in arsenate-containing medium was a function of the arsenate-to-P(i) ratio. Growth in arsenate-containing medium was not due to detoxification of the arsenate. Kinetic studies revealed that cells grown with a 10-fold excess of arsenate to P(i) have almost a twofold increase in capacity (V(max)) for P(i), but maintained the same affinity (K(m)). P(i) accumulation in the Pst-dependent strain was still sensitive to changes in the arsenate-to-P(i) ratio, and a K(i) (arsenate) for P(i) transport of 39 μM arsenate was determined. The Pst-dependent strain did not accumulate radioactive arsenate, and showed only a transient decrease in intracellular adenosine triphosphate levels after arsenate was added to the medium. The P(i) transport-dependent strain ceased growth in arsenate-containing media. This strain accumulated ⁷⁴As-arsenate, and intracellular adenosine triphosphate pools were almost completely depleted after the addition of arsenate to the medium. Arsenate accumulation required a metabolizable energy source and was inhibited by N-ethylmaleimide. Previously accumulated arsenate could exchange with arsenate or P(i) in the medium.