Isolation of Enterococcus hirae Mutant Deficient in Low-affinity Potassium Uptake at Alkaline pH

Abstract

  We here isolated an Enterococcus hirae mutant unable to grow well at pH 10. The influx rate calculated from steady-state ⁴²K⁺/K⁺ exchange and the intracellular K⁺ concentration of the mutant were reduced to 53 and 55% of those of the wild-type, respectively. The activities of two high-affinity K⁺ uptake systems, KtrI and KtrII, were normal in the mutant, but the kinetics of net K⁺ uptake at pH 10 indicated that a low-affinity K⁺ uptake with a K_m of about 20 mM (Kawano, M, Abuki, R, Igarashi, K, Kakinuma, Y. (2001) Arch. Microbiol. 175: 41-45), which were seen in the wild-type, was deficient in this mutant.