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Title: The discovery of phage-inducible chromosomal islands (PICIs) in Gram-negative bacteria
Author: Fillol Salom, Alfred
ISNI:       0000 0004 7655 3189
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2019
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Staphylococcus aureus pathogenicity islands (SaPIs) are highly mobile phage satellites that are intimately related to certain helper phages, whose life cycle they parasitise for their transfer to another bacterial hosts. As they encode virulence and fitness factors, this dissemination contributes to bacterial evolution, host adaptation and pathogenesis. During the last two decades, the relationship between SaPIs and helper phages has been studied, being the SaPIs one of the best characterised phage satellites. Recently, SaPI-like elements have been characterised in other Gram-positive species, constituting a new family of mobile genetic elements (MGEs): the phage inducible chromosomal islands (PICIs). PICIs are defined by the following features: exclusive attachment sites, unique genetic organisation, exclusive PICI genes, unique replicon, helper phage dependant induction and convergent mechanisms of phage interference. Based on the high prevalence of PICIs in Gram-positive bacteria, the presence of these MGEs in Gram-negative bacteria was studied. This study expands the PICI family to englobe, for the first time, members of Gram-negative bacteria. Using Escherichia coli and Pasteurella multocida as models, PICI elements present in these bacteria were characterised. During this study, a convergent mechanism of interference was perceived, the production of PICI-sized capsids. Furthermore, the prototypicle E. coli PICI, EcCICFT073, was identified as a cos PICI. This result, along with the recently characterised cos SaPIs, represents a paradigm shift involving cos phage in gene transfer. Additionally, a novel example of molecular parasitism was established, by which cos PICI elements encode a protein with a dual role, to block phage reproduction and to redirect phage packaging to promote their own transfer. Indeed, this is a one-shot strategy, highlighting PICIs as one of the most sophisticated parasites in nature. Overall, these results highlight the pervasive presence of PICI elements in Gram-negative bacteria, deciphering different strategies employed by these elements to achieve promiscuity in nature.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: QR Microbiology