On the Structural Transformations and Lysis of Halobacterium salinarium in Hypotonic and Isotonic Solution s

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Abstract
When the NaCl concentra-tion of a suspension of Halobacterium salinarium is gradually lowered by adding water, the rod-shaped organisms are converted to spheres which lyse. The organisms do not change in size when transformed from rods to spheres. Chemicals which do not possess a strong net charge in aqueous solutions do not protect the structure of the organism when they replace NaCl in iso-osmolar concentions. The rod shape of the organisms is only maintained by very high concentrations of ions which interact weakly with common proteins; lithium and ammonium ions are exceptions to this rule. Ions which display strong interactions with common proteins and chemicals which are believed to break secondary bonds between protein molecules effect a transformation of rods to spheres and frequently a lysis of the spheres when brought in contact with organisms suspended in strong NaCl solution. The changes in structure in hypotonic and isotonic solutions are not affected by metabolic inhibitors. Isolated cell-wall fragments disintegrate into smaller units when exposed to conditions under which whole organisms lyse. It is concluded that the structural transformations and lysis of H. salinarium in hypotonic solutions are not caused by the action of enzymes, and that osmotic phenomena play no or only a minor role. The observations support the contention that the globular lipoprotein particles which constitute the bulk of the material of the cell wall of these bacteria are bound together mainly by electrostatic forces and secondary bonds. When the cells are exposed to hypotonic solutions or to ions which bind strongly to proteins or to chemicals which are believed to break secondary bonds between protein molecules, the linkages binding the lipoprotein particles together are weakened so that the wall structure disintegrates. Only in the presence of high concentrations of sodium and chloride ions or other ions which bind loosely to proteins, is it possible for the proteinaceous particles of the cell wall to associate in an orderly array.