NapA Na⁺/H⁺ Antiporter as a Sodium Extrusion System Supplementary to the Vacuolar Na⁺-ATPase in Enterococcus hirae

Abstract

Enterococcus hirae has two sodium extrusion systems: the NapA Na⁺/H⁺ antiporter and the vacuolar Na⁺-ATPase. We found that a NapA mutant, WD4, which is deficient in Na⁺/H⁺ antiporter activity, grew well in the pH range of 6 to 10 up to 200 mM sodium. This was due to active, potential-independent sodium extrusion by the Na⁺-ATPase, which was induced under these conditions. The NapA Na⁺/H⁺ antiporter is thus not a prerequisite for growth of E. hirae in the presence of sodium, but plays a supplementary role in sodium extrusion at acidic pH.

• NapA
• Na⁺/H⁺ antiporter
• sodium extrusion
• vacuolar Na⁺-ATPase
• Enterococcus hirae