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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.
Insights
A Bacillus subtilis mutant shows defective lipid synthesis at high temperatures, leading to growth arrest and protein inclusions. This highlights the critical role of lipid synthesis in bacterial cell function.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Bacillus subtilis is a model organism for studying bacterial physiology.
- Temperature-sensitive mutants are valuable tools for dissecting essential cellular processes.
Purpose of the Study:
- To investigate the cellular defects in a temperature-sensitive Bacillus subtilis mutant at the non-permissive temperature.
- To identify the molecular basis of the pleiotropic phenotype observed in the mutant.
Main Methods:
- Culturing of Bacillus subtilis mutant at permissive and non-permissive temperatures (47 C).
- Monitoring bacterial growth, viability, and macromolecular synthesis (DNA, RNA, protein).
- Analysis of fatty acid composition and microscopy (phase-contrast, electron) to visualize inclusions.
Main Results:
- The mutant ceased growth and exhibited declining turbidity at 47 C, without immediate cell death or lysis.
- Deoxyribonucleic acid and ribonucleic acid synthesis halted, while protein synthesis continued at a reduced rate.
- Failure to alter fatty acid proportions and accumulation of membrane-associated protein inclusions were observed.
Conclusions:
- The temperature-sensitive phenotype is linked to a defect in lipid synthesis, impacting bacterial growth and cell integrity.
- Protein inclusions associated with membranes are a consequence of impaired lipid synthesis.
- Cellular processes like DNA and RNA synthesis are indirectly affected by the lipid synthesis defect.