Hijacking the hijackers: Escherichia coli phage-inducible chromosomal islands redirect lambda phage packaging for their own benefit

Abstract

Abstract de la comunicación oral presentada al 8th Congress of European Microbiologist. FEMS 2019. Glasgow, Scotland. 7-11 July 2019(Oral 098) Background: Phage-inducible chromosomal islands (PICIs) are clinically relevant mobile genetic elements widespread among Gram-positive and Gram-negative bacteria. Understanding the different PICI packaging mechanisms is essential to comprehend their intra- and inter-generic transfer, which contribute to bacterial evolution, host adaptation and pathogenesis. Objectives: Hijacking and blocking phage functions is vital for the PICI molecular pirates. They usually encode a battery of genetic resources to interfere with the phage. The objective of this study was to characterise the mechanism employed by EcCICFT073 to hijack the phage TerS, redirecting its affinity to package the PICI dsDNA. Methods: We identified by in vivo (phage evolution, genetic scarless mutations, competition assays) and in vitro (Two-hybrid assays, X-ray crystallography) experiments the molecular mechanism by which EcCICFT073 recruits the phage packaging machinery. Results: This study identified a novel and elegant one-shot strategy used by some cos lambda E. coli PICIs like EcCICFT073. Unlike other cos PICIs that carry the same phage cos sequence, EcCICFT073 carries the lambda phage cosQ and cosN, but a different cosB region (region involved in packaging initiation). Hence, these PICIs have developed a sophisticated strategy by encoding a protein, renamed as Rpp (Redirecting phage packaging) which forms a heterodimer with the phage TerS to perform dual roles: i) forming a new functional hetero DNA-binding (DBD) region that will be used to recognise the PICI cosB site; and ii) this new DBD would be unable to recognise the phage cos site, blocking phage packaging. This novel strategy highlights PICIs as sophisticated parasites in nature