Abstract
Bacteria and plants have some K+ transporters and K+ channels, which play important role in the adaptation of cells to hyperosmotic conditions. The ktrB gene isolated from Synechocystis PCC6803 was similar to Na+-K+ transporters (HKT/Ktr/Trk). Although wild-type of Synechocystis had K+ transport, the mutant disrupted ktrB gene did not show K+ transport. Moreover the mutant could not grow in the high salinity medium. Three Synechocystis genes, ktrA, ktrB and ktrE, were all required for K+ uptake. When ktrABE was expressed in K+ uptake deficient E.coli LB2003, this strain could grow under low K+ condition, and was detected Na+-dependent K+ uptake. Measurement of KtrABE transport in Synechocystis showed enhancement of K+ uptake in response to high osmolality challenge when Na+ was present in the medium, and that KtrABE prevented hyperosmotically-induced K+ loss from the cells. These data show that KtrABE functions as an essential mechanism in the adjustment to hyperosmolality stress.
