The TOL plasmid is naturally derepressed for transfer.

Area of Science:

• Microbiology
• Molecular Biology
• Bacteriology

Background:

• The TOL plasmid facilitates the degradation of aromatic hydrocarbons in Pseudomonas species.
• Plasmid-encoded pili play a role in bacterial conjugation and phage interactions.
• Differential gene expression can affect plasmid transfer and phenotypic characteristics.

Purpose of the Study:

• To investigate the expression state of the TOL plasmid in different Pseudomonas putida strains.
• To determine the correlation between TOL plasmid expression, pili formation, and bacteriophage susceptibility.
• To analyze the impact of host background on TOL plasmid transfer efficiency.

Main Methods:

• Bacteriophage lysis assays were performed on Pseudomonas putida strains harboring the TOL plasmid.
• Plasmid transfer frequencies were quantified on solid surfaces and in liquid media.
• Electron microscopy was used to visualize pili structures on bacterial cells.

Main Results:

• Pseudomonas putida strains mt-2 and AC37, carrying the TOL plasmid, were susceptible to lysis by bacteriophages PR4 and PRD1.
• Strain PpS388, also harboring the TOL plasmid, was resistant to these bacteriophages.
• TOL plasmid transfer was significantly higher in P. putida mt-2 compared to P. putida PpS388, indicating derepressed transfer in the former.
• Electron microscopy confirmed the presence of abundant, thick pili in TOL-expressing strains.

Conclusions:

• The TOL plasmid is constitutively expressed in P. putida strains mt-2 and AC37, leading to pili formation and phage susceptibility.
• TOL plasmid expression and transfer are repressed in P. putida strain PpS388.
• Host genetic background significantly influences TOL plasmid regulation and associated phenotypes.