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The TOL plasmid is naturally derepressed for transfer
Abstract:
Pseudomonas putida mt-2, formerly known as Pseudomonas arvilla mt-2, which carries the wild-type TOL plasmid, and P. putida strain AC37 carrying TOL, were completely lysed by the pilus-adsorbing plasmid-specific bacteriophages PR4 and PRD1. Pseudomonas putida strain PpS388, also harbouring the plasmid, was not lysed. In a P. putida mt-2 host, TOL transferred 18-fold better on a surface (2.5 X 10(-1) transconjugants per donor h-1) than in liquid; when P. putida PpS388 was the host, however, a frequency of only 2.3 X 10(-4) transconjugants per donor h-1 was obtained. Thus, TOL was derepressed for transfer in P. putida mt-2 and P. putida AC37, but not in P. putida PpS388. Electron microscopy revealed that TOL determined thick (8.5-10 nm diameter) flexible pili in large numbers, suggesting constitutive expression in its derepressed state.
Insights
The TOL plasmid in Pseudomonas putida strains mt-2 and AC37 was derepressed, leading to pili formation and susceptibility to bacteriophages. However, strain PpS388 showed repressed TOL plasmid transfer and pili expression.
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.