A microprobe analysis of inorganic elements in Halobacterium salinarum

Abstract

Halobacterium salinarum were grown on peptone agar containing 4.28 M NaCl, 0.036 M K and other salts. Stationary phase organisms were lifted onto carbon planchets, freeze-dried, carbon coated and examined in a scanning electron microscope equipped with an X-ray spectrometer. Intracellular element concentrations (mol/kg H(2)O) were determined using a bulk analysis program with appropriate standards. The cell K concentration was 110 times that of the medium. For Na this value was 0.3 and for Cl, 1.1. When Rb was present in the medium, its intracellular concentration was 77 times higher than the external value. The cation minus anion value suggests a high fixed negative charge, 0.72 equivalents. Intracellular apparent dielectric constants were calculated using cellular EMFs derived from the literature, and sodium concentration. The determined values ranged from 22-28 (vs 80 for normal water) suggesting phases of structured cell water. Ionic distributions in these extremophiles are treated according to the classical principles elucidated by Willard Gibbs and represents a heterogeneous system in thermodynamic equilibrium with the hypersaline environment. Factors to be considered are: (1) composition of Halobacterium and its immobile negative charge; (2) the physicochemical properties of the individual ions (charge, ionic radius, hydration energy, standard chemical potential); (3) the dielectric constant of the dispersion medium (water); and (4) the binding of ions, particularly potassium.

Circular Dichroism and Fluorescence Spectroscopy of Cysteinyl-tRNA Synthetase from Halobacterium salinarum ssp. NRC-1 Demonstrates that Group I Cations Are Particularly Effective in Providing Structure and Stability to This Halophilic Protein

“…The high effect of K + , then, may be due to evolutionary selection, since it is the most abundant cation in the intracellular environment of H. salinarum ssp. NRC-1 (4.7 M) [25], [26]. Studies of the Hofmeister effect on a halophilic malate dehydrogenase, found a similar order of stabilizing cations as the ones reported here [38].…”

An Extremely Halophilic Proteobacterium Combines a Highly Acidic Proteome with a Low Cytoplasmic Potassium Content

“…These results show that K ϩ is a major osmoprotectant in H. halophila, with Cl Ϫ being the major counterion, extending the use of KCl as a major osmoprotectant from the select group of the Halobacteria, Bacteroidetes (S. ruber), and Halanaerobiales to the Gammaproteobacteria. The highest reported cytoplasmic salt concentrations in these organisms are 1.9 M for Halanaerobium praevalens (8) and near 5.0 M for H. salinarum and S. ruber (9,10).…”

“…Extreme halophilicity in bacteria is less well studied but has been described for the chemotroph Salinibacter ruber and the photosynthetic purple bacterium Halorhodospira halophila (5, 6). A key factor in the halophilic adaptations of H. salinarum and S. ruber is that they accumulate up to 5 M KCl in their cytoplasm (7)(8)(9)(10)(11). This osmoprotection strategy results in unidentified protein-solvent interactions that drive a proteome-wide adaptation in which all proteins have an acidic isoelectric point due to an excess of Glu and Asp residues (4, 12-16).…”

A molecular perspective on the limits of life: Enzymes under pressure

“…nov., which grows optimally at 35 • C and better at 0.26 kbar than 1 bar [78]. In addition, the mesophilic Lactococcus lactis has been shown to accumulate sucrose and fructose at high pressures [27] and H. salinarum NRC-1, which accumulates high intracellular concentrations of K + and Cl − at similar molarity to hypersaline environments (∼ 4 M NaCl) [79], normally lives at atmospheric pressure but can survive pressures up to at least 4 kbar [28]. How-…”