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Streptococcus pneumoniae proteins released into medium upon inhibition of cell wall biosynthesis
Abstract:
Inhibition of murein biosynthesis in Streptococcus pneumoniae by either penicillin or bacitracin leads to an increase in the amount of protein secreted into the medium. This process was studied in wild-type cells grown under lysis-permissive conditions as well as in an autolysin-deficient mutant. The time course of secretion did not follow cellular lysis but commenced immediately after the addition of the cell wall inhibitor in a manner similar to that described recently for cell wall and membrane components in various tolerant streptococci. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that this increase was not due to the stimulation of release of three protein components which are secreted under normal growth conditions; rather, a complex set of cellular proteins escaped from the antibiotic-treated pneumococci. The proteins released during bacitracin treatment was slightly different from those observed when penicillin was used. Analysis on sucrose gradients indicated that the secreted proteins were membrane bound rather than soluble. Membrane vesicles could indeed be detected by electron microscopy of negative-stained secreted material.
Insights
Inhibiting murein biosynthesis in Streptococcus pneumoniae with antibiotics causes increased protein secretion. This released protein is membrane-bound, not soluble, and differs slightly between penicillin and bacitracin treatments.
Area of Science:
- Microbiology
- Cell Biology
- Biochemistry
Background:
- Murein biosynthesis is crucial for bacterial cell wall integrity.
- Streptococcus pneumoniae is a significant human pathogen.
- Antibiotic treatment can trigger cellular responses beyond direct killing.
Purpose of the Study:
- To investigate the phenomenon of increased protein secretion upon inhibition of murein biosynthesis in Streptococcus pneumoniae.
- To characterize the nature and origin of the secreted proteins.
- To compare the effects of different cell wall inhibitors (penicillin and bacitracin) on protein secretion.
Main Methods:
- Studying wild-type and autolysin-deficient Streptococcus pneumoniae strains.
- Utilizing cell wall inhibitors like penicillin and bacitracin.
- Employing Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) for protein analysis.
- Performing sucrose gradient centrifugation to determine protein solubility.
- Analyzing secreted material using electron microscopy.
Main Results:
- Inhibition of murein biosynthesis led to immediate and increased protein secretion, independent of cellular lysis.
- A complex set of cellular proteins, not previously secreted, was released.
- The protein release profile varied slightly between penicillin and bacitracin treatments.
- Secreted proteins were identified as membrane-bound, forming membrane vesicles.
Conclusions:
- Antibiotic-induced inhibition of murein synthesis triggers a non-lytic release of membrane-bound proteins in Streptococcus pneumoniae.
- The released proteins are a complex mixture, suggesting a broader cellular response to cell wall stress.
- This secretion mechanism may be conserved across different streptococcal species and cell wall inhibitors.