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Defective pyocin particles produced by some mutant strains of Pseudomonas aeruginosa
Abstract:
Mutants of Pseudomonas aeruginosa, defective in the production of active R-type pyocins, were isolated from pyocinogenic strains and their products were characterized. Polysheath-like structures were found in induced lysates of 29 out of 42 mutants. Two mutants (strain P15-16 and M189) were found to produce special defective particles, which were characterized in detail. The other 11 mutants did not produce significant amounts of any structure visible under an electron microscope. Serum blocking powers were found in lysates from P15-16 and M189 to significant amounts. Defective particle produced by strain P15-16 lacked the sheath component, whereas M189 had morphological defects at the junction between sheath and baseplate, and also in the architecture of baseplate. Both defective particles could adsorb to the surface of bacteria, that were sensitive to pyocin, at the tip of their fibers without killing cells. All M189 particles attached to the bacteria had the extended sheaths. Therefore, attachment to the bacteria by fibers is not sufficient to kill cells, and contraction of sheath must occur after the initial adsorption by fibers for pyocin to express its biological activity. Defective particles of strain P15-16, which was derived from strain P15 (a pyocin R1 producer), could be converted to active forms by an in vitro complementation reaction with extracts from certain mutants originated from strain PAO (a pyocin R2 producer). This result indicated the exchangeability of components between R-type pyocins belonging to the different groups.
Insights
Researchers studied Pseudomonas aeruginosa mutants lacking active R-type pyocins. Defective particles revealed that sheath contraction after fiber attachment is crucial for pyocin activity, and components are exchangeable between pyocin groups.
Area of Science:
- Microbiology
- Bacteriology
- Molecular Biology
Background:
- Pseudomonas aeruginosa produces R-type pyocins, bacteriocins that kill sensitive bacteria.
- Understanding pyocin structure and function is key to developing novel antimicrobial strategies.
Purpose of the Study:
- To characterize defective R-type pyocin particles produced by Pseudomonas aeruginosa mutants.
- To elucidate the mechanism of pyocin-mediated bacterial killing.
- To investigate the potential for component exchange between different R-type pyocin groups.
Main Methods:
- Isolation and characterization of pyocin-defective mutants of Pseudomonas aeruginosa.
- Electron microscopy to visualize pyocin structures in induced cell lysates.
- In vitro complementation assays to assess the exchangeability of pyocin components.
Main Results:
- Twenty-nine of 42 mutants produced polysheath-like structures; two produced unique defective particles (P15-16 and M189).
- Defective particles from P15-16 lacked sheaths, while M189 particles showed defects in sheath-baseplate junction and baseplate architecture.
- Both particle types adsorbed to sensitive bacteria via fibers without killing; M189 particles retained extended sheaths, indicating sheath contraction is necessary for activity.
Conclusions:
- Bacterial killing by R-type pyocins requires sheath contraction following initial adsorption by fibers.
- Components of R-type pyocins from different groups (R1 and R2) are exchangeable, suggesting conserved assembly mechanisms.