K + influx by Kup in Escherichia coli is accompanied by a decrease in H + efflux

Abstract

Escherichia coli accumulates K + by means of multiple uptake systems of which Kup is the major transport system at acidic pH. In cells grown under fermentative conditions at pH 5.5, K + influx by a wild-type strain upon hyper-osmotic stress at pH 5.5 was accompanied by a marked decrease in H + efflux, with a 1:1 ratio of K + to H + fluxes. This was observed with cells treated with N, N′-dicyclohexylcarbodiimide. Similar results with a mutant defective in Kdp and TrkA but with a functional Kup system but not in a mutant defective in Kdp and Kup but having an active TrkA system suggest that Kup operates as a H +–K +-symporter.