[Comparison of the lytic effect of gramicidin S and its derivatives on Bacillus megaterium and Micrococcus
Abstract:
Essential differences were found between the lytic action of gramicidin S. on Bacillus megaterium protoplasts and that on Micrococcus lysodeikticus protoplasts. When protoplasts were suspended in a sucrose solution in phosphate buffer, the lytic activity of gramicidin S toward B. megaterium protoplasts increased with a rise in the antibiotic concentration; the lytic action of gramicidin S on M. lysodeikticus protoplasts was characterized by a complex concentration dependence. Gramicidin S derivatives lacking basic properties since the amino groups of their ornithine residues were either substituted with urea residues (carbamoyl gramicidin) of acetylated (diacetyl gramicidin) showed a high lytic activity toward the both bacterial species. In contrast to gramicidin S, the derivatives virtually did not change the permeability of cytoplasmic membranes when they acted on intact cells. In the absence of phosphates (when protoplasts were suspended in an aqueous sucrose solution), the lytic activity of gramicidin S decreased while carbamoyl gramicidin and diacetyl gramicidin still were capable of causing lysis of M. lysodeikticus protoplasts though not of B. megaterium protoplasts.
Insights
Gramicidin S exhibits differential lytic activity against bacterial protoplasts. Modified gramicidin S derivatives show potent lysis without altering membrane permeability in intact cells.
Area of Science:
- Microbiology
- Biochemistry
- Molecular Biology
Background:
- Gramicidin S is a known antibiotic with lytic properties.
- Bacterial protoplasts offer a model system to study antibiotic mechanisms.
- Understanding gramicidin S's action on different bacterial species is crucial.
Purpose of the Study:
- To investigate the differential lytic effects of gramicidin S on Bacillus megaterium and Micrococcus lysodeikticus protoplasts.
- To evaluate the lytic activity of gramicidin S derivatives with modified basic properties.
- To compare the membrane permeability effects of gramicidin S and its derivatives on intact bacterial cells.
Main Methods:
- Preparation and treatment of bacterial protoplasts (Bacillus megaterium and Micrococcus lysodeikticus) with gramicidin S and its derivatives.
- Varying antibiotic concentrations and buffer conditions (presence/absence of phosphates).
- Assessing lytic activity and cytoplasmic membrane permeability changes.
Main Results:
- Gramicidin S displayed distinct concentration-dependent lytic activity against B. megaterium and M. lysodeikticus protoplasts.
- Carbamoyl gramicidin and diacetyl gramicidin (non-basic derivatives) showed high lytic activity against both species.
- Unlike gramicidin S, these derivatives minimally affected membrane permeability in intact cells.
- Phosphate presence influenced gramicidin S lytic activity, while derivatives retained lysis capability for M. lysodeikticus.
Conclusions:
- The basicity of gramicidin S influences its lytic mechanism and concentration dependence.
- Gramicidin S derivatives can retain potent lytic activity while exhibiting reduced membrane permeability effects.
- Phosphate ions modulate the interaction of gramicidin S with bacterial protoplasts.
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