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Colicin M is only bactericidal when provided from outside the cell
1Mikrobiologie II, Universität Tübingen, Federal Republic of Germany.
Abstract:
The colicin M structural gene, cma, was subcloned in a vector which allowed temperature-inducible control of its expression. Induction of expression of cma in colicin M uptake proficient strains was lethal for the host cell when the colicin M immunity protein was not present. In liquid culture cells lysed, and no colonies were formed on solid media. These effects were not observed in mutants defective in the colicin receptor (FhuA) or uptake functions (TonB, TolM), nor in wild-type cells treated with trypsin prior to induction of cma expression. It was concluded that cytoplasmic colicin M is not toxic for the producing cell. To exert a lethal effect the colicin has to enter the cell from outside. Cells expressing cma released small amounts of colicin M.
Insights
Colicin M is not toxic inside the cell. It must enter from outside to cause cell death, requiring specific uptake functions like FhuA and TonB.
Area of Science:
- Microbiology
- Molecular Biology
- Bacterial Genetics
Background:
- Colicin M is a bacteriocin produced by E. coli.
- Its mechanism of toxicity and cellular uptake are of significant interest.
- Understanding colicin activity is crucial for developing novel antimicrobial strategies.
Purpose of the Study:
- To investigate the conditions under which colicin M expression leads to host cell lethality.
- To determine if intracellularly produced colicin M is toxic to the producing cell.
- To elucidate the role of specific uptake proteins in colicin M-mediated cell death.
Main Methods:
- Subcloning the colicin M structural gene (cma) into a temperature-inducible expression vector.
- Expressing cma in various E. coli strains, including wild-type, immunity protein-deficient, and receptor/uptake mutants (FhuA, TonB, TolM).
- Assessing cell viability in liquid cultures and on solid media following cma induction; testing trypsin-treated cells.
Main Results:
- Induction of cma expression was lethal to host cells lacking the colicin M immunity protein, causing cell lysis and preventing colony formation.
- Lethality was dependent on functional colicin M uptake systems (FhuA, TonB, TolM).
- Mutants defective in these uptake functions, or wild-type cells treated with trypsin, did not exhibit cell death upon cma induction.
Conclusions:
- Cytoplasmic colicin M is not inherently toxic to the producing cell.
- Colicin M requires external entry into the cell via specific receptors and uptake machinery to exert its lethal effect.
- The study highlights the importance of the uptake pathway for colicin M's bacteriocin activity.