Antagonistic Effect of Monovalent Cations in Maintenance of Cellular Integrity of a Marine Bacterium

Abstract

The susceptibility of a marine bacterium, designated isolate c-A1, to lysis in distilled water and in salt solutions has been found to be a function of Na + concentration. Optical densities of cells pre-exposed to 0.05 m MgCl 2 were maintained in 1.0 m KCl, whereas those of cells pre-exposed to 1.0 m NaCl were not maintained at any KCl concentration tested. Cells transferred from MgCl 2 to low concentrations of NaCl underwent more extensive lysis than did those transferred to distilled water. The degree of disruption of cells transferred to distilled water from mixtures of 0.05 m MgCl 2 and NaCl (0 to 1.0 m ) was dependent on the concentration of NaCl; similar results were obtained with LiCl, but not with KCl. In electron micrographs of thin sections, c-A1 cell envelopes consisted of two double-track layers which fractured and peeled apart on lysis after pre-exposure to NaCl-MgCl 2 mixtures. Envelope eruptions or “hernias” occurred only in lysed cells pre-exposed to NaCl alone. No evidence for a functional lytic enzyme was found. Comparative studies on a terrestrial pseudomonad with a multilayered envelope indicated that preexposure to NaCl did not enhance the susceptibility of this cell to lysis in distilled water. The lytic susceptibility of the marine bacterium is considered to be the consequence of competition between specific monovalent cations and Mg ++ for electrostatic interactions with components of the cell envelope of this organism.