Summary: It is shown that possesses a Ca transporter, sensitive to the amiloride derivative 2”,4′-dimethylbenzamil (DMB), which is essential for grown at high Ca-concentrations, and which mediates the triggering by Ca of competence for genetic transformation in the exponential phase and autolysis in the late exponential phase. DMB inhibited both Ca transport and the Ca response. Kinetic analysis of Ca transport in ATP-depleted revealed an electrogenic influx sensitive to DMB. This transport was cooperative with respect to Ca concentration, and exhibited a Hill coefficient (nH) of 2. In bacteria pre-loaded with Ca, a DMB-sensitive efflux could be triggered by an imposed Na gradient. The efflux kinetics showed the same cooperativity profile as Ca concentration and a similar nH value to that of influx, suggesting a possible Na/Ca antiport. Cooperativity of transport was lowered (nH = 1) by a mutation that confers resistance to DMB and abolishes the Ca response. These results demonstrate that DMB-sensitive Ca transport is essential for growth and competence regulation. The role of the DMB-sensitive porter involved in Ca circulation and in Ca homeostasis and its possible regulation by competence factor are discussed.


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