The Na(+)-Responsive ntp Operon Is Indispensable for Homeostatis of K(+) and Na(+) in Enterococcus hirae at Limited Proton Potential

Enterococcus hirae ATCC 9790 grew well in Na(+)-deficient, low-K(+) medium, but growth was inhibited by carbonylcyanide m-chlorophenylhydrazone (CCCP). Growth inhibition and decrease of cellular K(+) levels in the presence of CCCP were relieved by the addition of Na(+) and a high concentration of K(+). In contrast, in the mutant defective in Na(+)-ATPase or the NtpJ component of the KtrII K(+) uptake system, CCCP-induced growth inhibition was rescued by a high concentration of K(+) but not of Na(+). These transporters are thus indispensable for homeostatis of K(+) and Na(+) at low proton potential.