Pulsed High-Field Gradient in Vivo NMR Spectroscopy to Measure Diffusional Water Permeability in Corynebacterium glutamicum

Abstract

Pulsed high-field gradient in vivo NMR spectroscopy was used to measure diffusional water permeability in cell suspensions of the Gram-positive bacterium Corynebacterium glutamicum. Two different regions of H2O mobility were detected. One was characterized by the apparent coefficient of self-diffusion, D1 app = (4.6–12.7) × 10−8 cm2 s−1, depending on the observation time t. The other region was characterized by D2 = 1.4 × 10−5 cm2 s−1. The value of D2 was similar to the diffusion coefficient of H2O in free water and in extracellular biological fluids. Restricted diffusion could be demonstrated for the slower process (D1). It was attributed to the cytoplasm of the cells. The membrane permeability, Pd H2O, for C. glutamicum was (4.8 ± 0.4) × 10−3 cm s−1. It compared favorably with values reported for human erythrocytes and was higher by a factor of about 100 compared to the diffusional permeability for ethanol, Pd ethanol, in Zymomonas mobilis. Addition of HgCl2, a water channel inhibitor in eukaryotes, decreased Pd H2O in C. glutamicum by a factor of ∼8. To our knowledge, these are the first functional studies of water transport in prokaryotes that yielded quantitative data, viz., transmembrane water permeability expressed through DH2O and Pd H2O.