Evidence for plasmid-mediated toxin production in Bacillus anthracis

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P Mikesell, B E Ivins, J D Ristroph

    Infection and Immunity
    |January 1, 1983
    PubMed

    Insights

    Bacillus anthracis virulence is linked to large plasmids encoding toxin production. Curing these plasmids eliminates toxin activity, which can be restored by reintroducing the plasmid DNA.

    Area of Science:

    • Microbiology
    • Molecular Biology
    • Bacterial Genetics

    Background:

    • Bacillus anthracis causes anthrax, a severe disease.
    • Toxin production is crucial for B. anthracis virulence.
    • The genetic basis for toxin production in B. anthracis was not fully understood.

    Purpose of the Study:

    • To investigate the role of plasmids in Bacillus anthracis toxin production.
    • To determine if specific plasmids are responsible for encoding toxin components.
    • To understand the genetic basis of B. anthracis virulence factors.

    Main Methods:

    • Isolation of large-molecular-weight plasmids from virulent and avirulent B. anthracis strains.
    • Curing bacterial strains of plasmids by heat passage (42.5°C).
    • Assessing toxin activity (lethal toxin, edema-producing activity, lethal factor, protective antigen) before and after curing.
    • Transformation of cured strains with purified plasmid DNA to restore toxin production.

    Main Results:

    • Each B. anthracis strain possessed a unique plasmid species.
    • Curing strains of plasmids resulted in a loss of toxin production and serological activities.
    • Transformation experiments restored toxin production and confirmed plasmid involvement.
    • Nontoxigenic Pasteur vaccine strains lacked detectable plasmids.

    Conclusions:

    • Large plasmids in B. anthracis are essential for toxin production.
    • These plasmids likely encode structural or regulatory proteins for toxin synthesis.
    • The findings support the hypothesis that Pasteur likely cured B. anthracis of temperature-sensitive plasmids responsible for toxin production.

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