Related Experiment Videos
Polycations which disorganize the outer membrane inhibit conjugation in Escherichia coli
Abstract:
Outer membrane disorganizing polycation, polymyxin B nonapeptide (PMBN), reduced drastically the production of recombinants when present at sub-MIC concentrations during F'-mediated Escherichia coli conjugation. The decrease of recombinants was accompanied by a less marked decrease of viability in the recipient population in a manner resembling lethal zygosis. No reduction was seen when either donor or recipient was grown in the same PMBN concentration, washed and resuspended to PMBN-free medium before mating. The same concentration of outer membrane disorganizing polycations of higher bactericidal activity (protamine and polylysine) caused only a moderate reduction in transconjugant frequency when present during mating. Spermine and tetralysine, which are not effective disorganizers of the outer membrane, did not reduce the recombinant frequency or the viability of the recipients.
Insights
Polymyxin B nonapeptide (PMBN) significantly hinders bacterial conjugation by disrupting the outer membrane. This impacts recombinant production and recipient viability, suggesting a novel mechanism beyond simple toxicity.
Area of Science:
- Microbiology
- Molecular Biology
- Bacterial Genetics
Background:
- Bacterial conjugation is a key mechanism for horizontal gene transfer.
- Polycations can interact with bacterial outer membranes, affecting cell integrity and function.
- Polymyxin B nonapeptide (PMBN) is known to disorganize bacterial outer membranes.
Purpose of the Study:
- To investigate the effect of PMBN on F'-mediated Escherichia coli conjugation.
- To determine if PMBN's outer membrane disorganizing property influences conjugation efficiency.
- To compare PMBN's effect with other polycations of varying membrane activity.
Main Methods:
- Escherichia coli conjugation experiments were performed with F' plasmids.
- Varying concentrations of PMBN and other polycations were added during mating.
- Recombinant frequencies and recipient viability were quantified.
- Experiments included pre-treatment and washing steps to assess PMBN's role during mating.
Main Results:
- Sub-inhibitory concentrations of PMBN drastically reduced recombinant production during conjugation.
- PMBN also decreased recipient viability, mimicking lethal zygosis.
- No reduction in recombinants occurred if cells were pre-treated and washed, indicating PMBN acts during mating.
- Other potent outer membrane disorganizers (protamine, polylysine) caused only moderate reductions.
- Non-disorganizing polycations (spermine, tetralysine) had no effect on recombinant frequency or viability.
Conclusions:
- PMBN significantly inhibits bacterial conjugation, likely through its outer membrane disorganizing activity during the mating process.
- The observed reduction in viability suggests PMBN interferes with essential cellular processes during conjugation.
- PMBN's specific mechanism of inhibiting conjugation differs from its general bactericidal activity and that of other polycations.