AUTHOR=Valero-Rello Ana , López-Sanz María , Quevedo-Olmos Alvaro , Sorokin Alexei , Ayora Silvia 

TITLE=Molecular Mechanisms That Contribute to Horizontal Transfer of Plasmids by the Bacteriophage SPP1

JOURNAL=Frontiers in Microbiology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2017.01816

DOI=10.3389/fmicb.2017.01816

ISSN=1664-302X

ABSTRACT=<p>Natural transformation and viral-mediated transduction are the main avenues of horizontal gene transfer in Firmicutes. <italic>Bacillus subtilis</italic> SPP1 is a generalized transducing bacteriophage. Using this lytic phage as a model, we have analyzed how viral replication and recombination systems contribute to the transfer of plasmid-borne antibiotic resistances. Phage SPP1 DNA replication relies on essential phage-encoded replisome organizer (G<italic>38</italic>P), helicase loader (G<italic>39</italic>P), hexameric replicative helicase (G<italic>40</italic>P), recombinase (G<italic>35</italic>P) and in less extent on the partially dispensable 5′→3′ exonuclease (G<italic>34</italic>.<italic>1</italic>P), the single-stranded DNA binding protein (G<italic>36</italic>P) and the Holliday junction resolvase (G<italic>44</italic>P). Correspondingly, the accumulation of linear concatemeric plasmid DNA, and the formation of transducing particles were blocked in the absence of G<italic>35</italic>P, G<italic>38</italic>P, G<italic>39</italic>P, and G<italic>40</italic>P, greatly reduced in the G<italic>34</italic>.<italic>1</italic>P, G<italic>36</italic>P mutants, and slightly reduced in G<italic>44</italic>P mutants. In contrast, establishment of injected linear plasmid DNA in the recipient host was independent of viral-encoded functions. DNA homology between SPP1 and the plasmid, rather than a viral packaging signal, enhanced the accumulation of packagable plasmid DNA. The transfer efficiency was also dependent on plasmid copy number, and rolling-circle plasmids were encapsidated at higher frequencies than theta-type replicating plasmids.</p>