Potassium uptake in the unicellular cyanobacterium Synechocystis sp. strain PCC 6803 mainly depends on a Ktr-like system encoded by slr1509 (ntpJ).

The molecular basis of potassium uptake in cyanobacteria has not been elucidated. However, genes known from other bacteria to encode potassium transporters can be identified in the genome of Synechocystis sp. strain PCC 6803. Mutants defective in kdpA and ntpJ were generated and characterized to address the role of the Kdp and KtrAB systems in this strain. KtrAB is crucial for K(+) uptake, as the DeltantpJ mutant shows slowed growth, slowed potassium uptake kinetics, and increased salt sensitivity. The DeltakdpA mutant has the same phenotype as the wild type even at limiting potassium, but a DeltakdpADeltantpJ double mutant is not viable, indicating a role of Kdp for potassium uptake when the Ktr system is not functioning.