23Na NMR study of Fibrobacter succinogenes S85: comparison of three chemical shift reagents and calculation of sodium concentration using ionophores.

In order to measure intracellular sodium concentrations in resting cells of Fibrobacter succinogenes S85 by (23)Na NMR spectrometry, two methodological aspects were studied. First, three different shift reagents (Dy(PPP(i))(7-)(2), Tm(DOTP)(5-), and Dy(TTHA)(3-)) were tested for their ability to separate internal and external (23)Na NMR resonances. Their toxicity toward F. succinogenes cells was evaluated by in vivo(13)C NMR experiments. Tm(DOTP)(5-) was found to be the most efficient shift reagent while being nontoxic. Second, a new methodology was developed to calculate intracellular sodium concentration in F. succinogenes by using ionophores. This approach avoided the problem of intracellular volume measurement and that of sodium visibility determination.