The Na(+) transport in Gram-positive bacteria defect in the Mrp antiporter complex measured with (23)Na-NMR.

(23)Na-NMR has previously been used to monitor Na(+) translocation across membranes in Gram-negative bacteria and in various other organelles and liposomes using a membrane-impermeable shift reagent to resolve the signals resulting from internal and external Na(+). In this work, the (23)Na-NMR method was adapted for measurements of internal Na(+) concentration in the Gram-positive bacterium Bacillus subtilis, with the aim of assessing the Na(+) translocation activity of the Mrp antiporter complex, a member of the Cation Proton Antiporter-3 (CPA-3) family. The sodium sensitive growth phenotype observed in a B. subtilis strain with the gene encoding MrpA deleted, could indeed be correlated to the inability of this strain to maintain a lower internal than external Na(+) concentration.