Thallous ion is accumulated by potassium transport systems in Escherichia coli

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Abstract
The accumulation of 204Tl+ by E. coli occurs primarily via either of 2 K+ transport systems called Kdp and TrkA. Tl+ influx is inhibited and Tl+ efflux is stimulated by the addition of K+ to the assay medium. Mutants defective in both the Kdp and TrkA systems accumulate little Tl+. Uptake of triphenylmethylphosphonium, a lipid-soluble cation whose distribution is widely used to estimate the membrane electrical potential in bacteria, occurs to about the same extent in mutants that accumulate little Tl+ as in strains that accumulate Tl+ to high levels. Tl+ may be useful as a probe of bacterial K+ transport systems but is not a reliable indicator of the membrane electrical potential in E. coli.