Temperature-Sensitive Mutant of Bacillus subtilis That Accumulates Membrane-Associated Protein Inclusions

Abstract

At 47 C, a temperature-sensitive mutant of Bacillus subtilis 168 accumulates membrane-associated protein inclusions and exhibits a pleiotropic phenotype indicative of a defect in lipid synthesis. The mutant bacteria cease growing at 47 C, and the turbidity of the culture gradually declines. The lack of growth is not due to the death or lysis of the cells, since viability does not decrease for about 1 hr and the “lysis” can be delayed for several hours by increasing the osmotic pressure of the medium. Synthesis of deoxyribonucleic acid and ribonucleic acid stops at 47 C although a residual synthesis of protein occurs. When the temperature is raised, the mutant fails to increase the proportion of 17:0 branched-chain fatty acids and to decrease the proportion of 18:0 and 18:1 fatty acids. The membrane-associated inclusions can be seen by phase-contrast or electron microscopy and remain attached to protoplast membranes during isolation. The inclusions are mostly protein and are digested with Pronase.