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Viral evasion of a bacterial suicide system by RNA-based molecular mimicry enables infectious altruism.

Blower TR, Evans TJ, Przybilski R, Fineran PC, Salmond GP - PLoS Genet. (2012)

Bottom Line: The ΦTE escape mutants had expanded the number of these "pseudo-ToxI" genetic repeats and, in one case, an escape phage had "hijacked" ToxI from the plasmid-borne toxIN locus, through recombination.This is the first example of a non-coding RNA encoded by a phage that evolves by selective expansion and recombination to enable viral suppression of a defensive bacterial suicide system.Furthermore, the ΦTE escape phages had evolved enhanced capacity to transduce replicons expressing ToxIN, demonstrating virus-mediated horizontal transfer of genetic altruism.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom.

ABSTRACT
Abortive infection, during which an infected bacterial cell commits altruistic suicide to destroy the replicating bacteriophage and protect the clonal population, can be mediated by toxin-antitoxin systems such as the Type III protein-RNA toxin-antitoxin system, ToxIN. A flagellum-dependent bacteriophage of the Myoviridae, ΦTE, evolved rare mutants that "escaped" ToxIN-mediated abortive infection within Pectobacterium atrosepticum. Wild-type ΦTE encoded a short sequence similar to the repetitive nucleotide sequence of the RNA antitoxin, ToxI, from ToxIN. The ΦTE escape mutants had expanded the number of these "pseudo-ToxI" genetic repeats and, in one case, an escape phage had "hijacked" ToxI from the plasmid-borne toxIN locus, through recombination. Expression of the pseudo-ToxI repeats during ΦTE infection allowed the phage to replicate, unaffected by ToxIN, through RNA-based molecular mimicry. This is the first example of a non-coding RNA encoded by a phage that evolves by selective expansion and recombination to enable viral suppression of a defensive bacterial suicide system. Furthermore, the ΦTE escape phages had evolved enhanced capacity to transduce replicons expressing ToxIN, demonstrating virus-mediated horizontal transfer of genetic altruism.

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Only the recombinant ΦTE-F escape locus can replace ToxI in the native ToxIN locus.(A) Organisation of the ToxIN operon. Promoter elements are shown as black boxes. The transcriptional start site is indicated by the arrow with ‘+1’. The 5.5 repeats of toxI are followed by a stem-loop terminator structure, then toxN. It was possible to excise the full toxI sequence and then attempt to replace it with the escape locus sequences, including the invariant ends, from ΦTE wt, ΦTE-A and ΦTE-F, as shown in Figure 2. (B) The single plasmid that could be successfully generated, which included the insert from ΦTE-F, was tested for Abi activity against ΦS61 and seen to be highly active.
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pgen-1003023-g005: Only the recombinant ΦTE-F escape locus can replace ToxI in the native ToxIN locus.(A) Organisation of the ToxIN operon. Promoter elements are shown as black boxes. The transcriptional start site is indicated by the arrow with ‘+1’. The 5.5 repeats of toxI are followed by a stem-loop terminator structure, then toxN. It was possible to excise the full toxI sequence and then attempt to replace it with the escape locus sequences, including the invariant ends, from ΦTE wt, ΦTE-A and ΦTE-F, as shown in Figure 2. (B) The single plasmid that could be successfully generated, which included the insert from ΦTE-F, was tested for Abi activity against ΦS61 and seen to be highly active.

Mentions: Finally, in attempts to generate a more native context, the escape loci from ΦTE wt, ΦTE-A and ΦTE-F were cloned to replace ToxI within the native toxIN operon (Figure 5A). This cloning required the use of a transposon-marked derivative of the original ToxIN plasmid, pECA1039-Km3 [11]. In this case, only recombinants with the insert from ΦTE-F could be obtained, presumably due to toxic effects preventing cloning of ΦTE wt and ΦTE-A. The ΦTE-F plasmid retained Abi activity (Figure 5B), as tested with ΦS61 [12], which was used in order to prevent any possible interaction of an infecting ΦTE with the regions of the ΦTE genome cloned onto the test plasmid construct.


Viral evasion of a bacterial suicide system by RNA-based molecular mimicry enables infectious altruism.

Blower TR, Evans TJ, Przybilski R, Fineran PC, Salmond GP - PLoS Genet. (2012)

Only the recombinant ΦTE-F escape locus can replace ToxI in the native ToxIN locus.(A) Organisation of the ToxIN operon. Promoter elements are shown as black boxes. The transcriptional start site is indicated by the arrow with ‘+1’. The 5.5 repeats of toxI are followed by a stem-loop terminator structure, then toxN. It was possible to excise the full toxI sequence and then attempt to replace it with the escape locus sequences, including the invariant ends, from ΦTE wt, ΦTE-A and ΦTE-F, as shown in Figure 2. (B) The single plasmid that could be successfully generated, which included the insert from ΦTE-F, was tested for Abi activity against ΦS61 and seen to be highly active.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3475682&req=5

pgen-1003023-g005: Only the recombinant ΦTE-F escape locus can replace ToxI in the native ToxIN locus.(A) Organisation of the ToxIN operon. Promoter elements are shown as black boxes. The transcriptional start site is indicated by the arrow with ‘+1’. The 5.5 repeats of toxI are followed by a stem-loop terminator structure, then toxN. It was possible to excise the full toxI sequence and then attempt to replace it with the escape locus sequences, including the invariant ends, from ΦTE wt, ΦTE-A and ΦTE-F, as shown in Figure 2. (B) The single plasmid that could be successfully generated, which included the insert from ΦTE-F, was tested for Abi activity against ΦS61 and seen to be highly active.
Mentions: Finally, in attempts to generate a more native context, the escape loci from ΦTE wt, ΦTE-A and ΦTE-F were cloned to replace ToxI within the native toxIN operon (Figure 5A). This cloning required the use of a transposon-marked derivative of the original ToxIN plasmid, pECA1039-Km3 [11]. In this case, only recombinants with the insert from ΦTE-F could be obtained, presumably due to toxic effects preventing cloning of ΦTE wt and ΦTE-A. The ΦTE-F plasmid retained Abi activity (Figure 5B), as tested with ΦS61 [12], which was used in order to prevent any possible interaction of an infecting ΦTE with the regions of the ΦTE genome cloned onto the test plasmid construct.

Bottom Line: The ΦTE escape mutants had expanded the number of these "pseudo-ToxI" genetic repeats and, in one case, an escape phage had "hijacked" ToxI from the plasmid-borne toxIN locus, through recombination.This is the first example of a non-coding RNA encoded by a phage that evolves by selective expansion and recombination to enable viral suppression of a defensive bacterial suicide system.Furthermore, the ΦTE escape phages had evolved enhanced capacity to transduce replicons expressing ToxIN, demonstrating virus-mediated horizontal transfer of genetic altruism.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom.

ABSTRACT
Abortive infection, during which an infected bacterial cell commits altruistic suicide to destroy the replicating bacteriophage and protect the clonal population, can be mediated by toxin-antitoxin systems such as the Type III protein-RNA toxin-antitoxin system, ToxIN. A flagellum-dependent bacteriophage of the Myoviridae, ΦTE, evolved rare mutants that "escaped" ToxIN-mediated abortive infection within Pectobacterium atrosepticum. Wild-type ΦTE encoded a short sequence similar to the repetitive nucleotide sequence of the RNA antitoxin, ToxI, from ToxIN. The ΦTE escape mutants had expanded the number of these "pseudo-ToxI" genetic repeats and, in one case, an escape phage had "hijacked" ToxI from the plasmid-borne toxIN locus, through recombination. Expression of the pseudo-ToxI repeats during ΦTE infection allowed the phage to replicate, unaffected by ToxIN, through RNA-based molecular mimicry. This is the first example of a non-coding RNA encoded by a phage that evolves by selective expansion and recombination to enable viral suppression of a defensive bacterial suicide system. Furthermore, the ΦTE escape phages had evolved enhanced capacity to transduce replicons expressing ToxIN, demonstrating virus-mediated horizontal transfer of genetic altruism.

Show MeSH
Related in: MedlinePlus