Two major potassium uptake systems, KtrI and KtrII, inEnterococcus hirae

We isolated a mutant, JEMK1, which did not grow at pH 6.0 in medium containing 0.5 mM KCl, derived from a Enterococcus hirae mutant deficient in the KtrII K+ uptake system. This mutant showed an impairment in the proton potential-dependent K+ uptake, the activity of the KtrI K+ uptake system, and did not grow well in K+-poor media in a wide pH range from 6 to 10, suggesting that KtrI and KtrII are the main systems for potassium accumulation of this bacterium.