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Action of penicillin G on endosymbiote lambda particles of Paramecium aurelia
Abstract:
The kinetics of loss from the cytoplasm and changes in ultrastructure of symbiont lambda particles after treatment of axenically cultivated lambda-bearing Paramecium aurelia with penicillin G was investigated. Low concentrations (1 to 2 unit/ml) of the antibiotic caused many particles within the cell to become filamentous; high concentrations (2,000 unit/ml) caused lysis of the particles without noticeably affecting the protozoan. The ED(50) value (2 to 3 unit/ml) was within the range of values found to cause lysis of many gram-negative bacteria. Rapidly dividing lambda were more vulnerable to the action of the antibiotic than slowly dividing particles. Nondividing particles were not affected by exposure to the antibiotic. Ultrastructural changes observed in lambda during lysis by penicillin G were consistent with the view that penicillin interferes with the synthesis of a vital component of the cell envelope of the particle, possibly a peptidoglycan similar to that found in the cell walls of bacteria. The deoxyribonucleic acid of lambda was dispersed throughout the particle as electron dense fibers enclosed within electron transparent areas. The cell envelope appeared to consist of at least two morphologically distinguishable layers, an inner layer homologous to the plasma membrane of bacteria and an outer layer homologous to the bacterial cell wall. Lambda may be regarded as a randomly distributed population of bacteria growing and dividing synchronously within the collective cytoplasm of its protozoan host.
Insights
Penicillin G affects symbiont lambda particles in Paramecium aurelia, causing filamentous changes at low doses and lysis at high doses. Rapidly dividing lambda are most susceptible, suggesting interference with cell envelope synthesis.
Area of Science:
- Microbiology
- Cell Biology
- Symbiosis
Background:
- Symbiont lambda particles reside within the cytoplasm of Paramecium aurelia.
- The nature of lambda particles suggests a bacterial origin, potentially with a cell wall.
- Understanding symbiont-host interactions is crucial for cellular biology.
Purpose of the Study:
- To investigate the effects of penicillin G on lambda particles within Paramecium aurelia.
- To determine the susceptibility of lambda particles to penicillin G based on their division rate.
- To elucidate the mechanism of penicillin G action on lambda particle ultrastructure and cell envelope.
Main Methods:
- Treatment of axenically cultivated lambda-bearing Paramecium aurelia with varying concentrations of penicillin G.
- Microscopic examination of changes in lambda particle ultrastructure and distribution.
- Determination of the effective dose 50 (ED(50)) for penicillin G action on lambda particles.
Main Results:
- Low penicillin G concentrations (1-2 U/ml) induced filamentous changes in lambda particles.
- High penicillin G concentrations (2,000 U/ml) caused lysis of lambda particles without harming the protozoan host.
- The ED(50) was 2-3 U/ml, similar to that for gram-negative bacteria; rapidly dividing lambda were more sensitive.
- Ultrastructural analysis indicated penicillin G interferes with cell envelope synthesis, possibly involving peptidoglycan.
Conclusions:
- Penicillin G effectively targets symbiont lambda particles in Paramecium aurelia, with differential effects based on concentration and particle division rate.
- The observed ultrastructural changes suggest that lambda particles possess a cell envelope, potentially including peptidoglycan, similar to bacteria.
- Lambda particles can be considered analogous to bacteria undergoing synchronous growth and division within their protozoan host.