Biodiversity of lactococcal bacteriophages and associated phage-host interactions

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Oliveira, Joana
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University College Cork
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Lactococcus lactis represents one of the most intensely exploited species of lactic acid bacteria (LAB) for dairy fermentations. The intensive and repeated application of lactococcal strains or strain blends in dairy fermentations creates a favourable environment for the proliferation of (bacterio)phages. Members of three lactococcal phage groups are the most frequently encountered in the dairy industry, namely phages belonging to the 936, c2 and P335 groups, which together pose a considerable threat to product quality and consistency. In this thesis, a collection of one hundred and thirty seven lactococcal phages was generated following their isolation from distinct dairy fermentation facilities worldwide. Using multiplex PCR (i) the three main lactococcal phage groups were identified and the relative abundance of the 936 (59.85 %), c2 (15.33 %) and P335 (24.82 %) phages was defined, while (ii) the cell wall polysaccharide (CWPS) genotype of one hundred and thirteen lactococcal strains was also defined in an effort to correlate phage sensitivity profiles to specific CWPS types. Furthermore, the identification of a small number of phage-resistant strains prompted a genomic investigation of the plasmid-encoded phage-resistance mechanisms followed by conjugation experiments to investigate the functionality of the predicted gene transfer functions identified in our lactococcal plasmid collection. Finally, the potential application of flow cytometry for the detection and enumeration of phages was evaluated, and its accuracy was compared with traditional methods such as the double-agar plaque assay. This thesis represents one of the largest phage-host surveys undertaken in recent years. The resulting information has expanded current knowledge on prevalent phage groups in industrial fermentations and their interactions with their hosts. It is envisaged that the combined approaches to evaluate phage biodiversity and tools to detect and prevent their proliferation will support current and future needs of the dairy industry.
Lactococcus lactis , Lactococcal bacteriophage
Oliveira, J. 2017. Biodiversity of lactococcal bacteriophages and associated phage-host interactions. PhD Thesis, University College Cork.