Neutron scattering reveals extremely slow cell water in a Dead Sea organism

doi:10.1073/pnas.0601639104

Neutron scattering reveals extremely slow cell water in a Dead Sea organism

*Institut de Biologie Structurale, Commissariat à l'Energie Atomique–Centre National de la Recherche Scientifique–Université Joseph Fourier, Laboratoire de Biophysique Moléculaire, 41 Rue Jules Horowitz, 38027 Grenoble Cedex 1, France;
^‡Institut Laue Langevin, 6 Rue Jules Horowitz BP 156, 38042 Grenoble Cedex 9, France;
^§Max-Planck-Institut für Biochemie, Abteilung, Membranbiochemie, Am Klopferspitz 18, 82152 Martinsried, Germany;
^¶Institut für Festkoerperforschung Forschungszentrum Juelich GmbH D-52425 Juelich, Germany; and
**Plant Biophysical Laboratory, Institute of Life Sciences, The Hebrew University, Givat Ram, Jerusalem 91904, Israel

Edited by H. Eugene Stanley, Boston University, Boston, MA, and approved November 21, 2006 (received for review February 28, 2006)

Abstract

Intracellular water dynamics in Haloarcula marismortui, an extremely halophilic organism originally isolated from the Dead Sea, was studied by neutron scattering. The water in centrifuged cell pellets was examined by means of two spectrometers, IN6 and IN16, sensitive to motions with time scales of 10 ps and 1 ns, respectively. From IN6 data, a translational diffusion constant of 1.3 × 10⁻⁵ cm² s⁻¹ was determined at 285 K. This value is close to that found previously for other cells and close to that for bulk water, as well as that of the water in the 3.5 M NaCl solution bathing the cells. A very slow water component was discovered from the IN16 data. At 285 K the water-protons of this component displays a residence time of 411 ps (compared with a few ps in bulk water). At 300 K, the residence time dropped to 243 ps and was associated with a translational diffusion of 9.3 × 10⁻⁸ cm² s⁻¹, or 250 times lower than that of bulk water. This slow water accounts for ≈76% of cell water in H. marismortui. No such water was found in Escherichia coli measured on BSS, a neutron spectrometer with properties similar to those of IN16. It is hypothesized that the slow mobility of a large part of H. marismortui cell water indicates a specific water structure responsible for the large amounts of K⁺ bound within these extremophile cells.

Footnotes

^‖To whom correspondence should be addressed. E-mail: zaccai{at}ill.fr
Author contributions: M.T., B.F., F.G., E.F., D.O., G.Z., M.G., and B.-Z.G. designed research; M.T., B.F., K.W., F.G., M.J., M.Z., D.O., G.Z., M.G., and B.-Z.G. performed research; M.T., B.F., F.G., M.J., M.Z., D.O., and G.Z. contributed new reagents/analytic tools; M.T., K.W., E.F., and G.Z. analyzed data; and M.T., B.F., G.Z., M.G., and B.-Z.G. wrote the paper.
↵ ^†Present address: Institut Laue Langevin, 6 Rue Jules Horowitz, BP 156, 38042 Grenoble Cedex 9, France.
The authors declare no conflict of interest.
This article is a PNAS direct submission.
Abbreviation:

QENS,

quasielastic neutron scattering.