Emergence of a Competence-Reducing Filamentous Phage from the Genome of Acinetobacter baylyi ADP1.
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ABSTRACT: Bacterial genomes commonly contain prophage sequences as a result of past infections with lysogenic phages. Many of these integrated viral sequences are believed to be cryptic, but prophage genes are sometimes coopted by the host, and some prophages may be reactivated to form infectious particles when cells are stressed or mutate. We found that a previously uncharacterized filamentous phage emerged from the genome of Acinetobacter baylyi ADP1 during a laboratory evolution experiment. This phage has a genetic organization similar to that of the Vibrio cholerae CTX? phage. The emergence of the ADP1 phage was associated with the evolution of reduced transformability in our experimental populations, so we named it the competence-reducing acinetobacter phage (CRA?). Knocking out ADP1 genes required for competence leads to resistance to CRA? infection. Although filamentous bacteriophages are known to target type IV pili, this is the first report of a phage that apparently uses a competence pilus as a receptor. A. baylyi may be especially susceptible to this route of infection because every cell is competent during normal growth, whereas competence is induced only under certain environmental conditions or in a subpopulation of cells in other bacterial species. It is possible that CRA?-like phages restrict horizontal gene transfer in nature by inhibiting the growth of naturally transformable strains. We also found that prophages with homology to CRA? exist in several strains of Acinetobacter baumannii These CRA?-like A. baumannii prophages encode toxins similar to CTX? that might contribute to the virulence of this opportunistic multidrug-resistant pathogen.We observed the emergence of a novel filamentous phage (CRA?) from the genome of Acinetobacter baylyi ADP1 during a long-term laboratory evolution experiment. CRA? is the first bacteriophage reported to require the molecular machinery involved in the uptake of environmental DNA for infection. Reactivation and evolution of CRA? reduced the potential for horizontal transfer of genes via natural transformation in our experiment. Risk of infection by similar phages may limit the expression and maintenance of bacterial competence in nature. The closest studied relative of CRA? is the Vibrio cholerae CTX? phage. Variants of CRA? are found in the genomes of Acinetobacter baumannii strains, and it is possible that phage-encoded toxins contribute to the virulence of this opportunistic multidrug-resistant pathogen.
SUBMITTER: Renda BA
PROVIDER: S-EPMC5105901 | biostudies-literature | 2016 Dec
REPOSITORIES: biostudies-literature
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