A novel lysis system in PM2, a lipid-containing marine double-stranded DNA bacteriophage

Authors

  • Mart Krupovič,

    1. Department of Biological and Environmental Sciences and Institute of Biotechnology, Biocenter 2, PO Box 56 (Viikinkaari 5), 00014 University of Helsinki, Finland.
    2. Department of Biochemistry and Biophysics, Vilnius University, M. K. Čiurlionio 21, 03101 Vilnius, Lithuania.
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  • Rimantas Daugelavičius,

    1. Department of Biological and Environmental Sciences and Institute of Biotechnology, Biocenter 2, PO Box 56 (Viikinkaari 5), 00014 University of Helsinki, Finland.
    2. Department of Biochemistry and Biophysics, Vilnius University, M. K. Čiurlionio 21, 03101 Vilnius, Lithuania.
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  • Dennis H. Bamford

    Corresponding author
    1. Department of Biological and Environmental Sciences and Institute of Biotechnology, Biocenter 2, PO Box 56 (Viikinkaari 5), 00014 University of Helsinki, Finland.
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E-mail dennis.bamford@helsinki.fi; Tel. (+358) 9 191 59100; Fax (+358) 9 191 59098.

Summary

In this study we investigated the lysis system of the lipid-containing double-stranded DNA bacteriophage PM2 infecting Gram-negative marine Pseudoalteromonas species. We analysed wt and lysis-deficient phage-induced changes in the host physiology and ascribed functions to two PM2 gene products (gp) involved in lysis. We show that bacteriophage PM2 uses a novel system to disrupt the infected cell. The novelty is based on the following findings: (i) gp k is needed for the permeabilization of the cytoplasmic membrane and appears to play the role of a typical holin. However, its unique primary structure [53 aa, 1 transmembrane domain (TMD)] places it into a new class of holins. (ii) We have proposed that, unlike other bacteriophages studied, PM2 relies on lytic factors of the cellular origin for digestion of the peptidoglycan. (iii) gp l (51 aa, no TMDs) is needed for disruption of the outer membrane, which is highly rigidified by the divalent cations abundant in the marine environment. The gp l has no precedent in other phage lytic systems studied so far. However, the presence of open reading frame l-like genes in genomes of other bacterial viruses suggests that the same system might be used by other phages and is not unique to PM2.

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