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Panagiotis Kalatzis:
Bacteriophage interactions with marine pathogenic Vibrios

Date: 01-10-2017    Supervisor: Mathias Middelboe

Incidents of Vibrio-associated diseases in marine aquaculture are increasingly reported on a global scale, incited also by the world’s rising temperature. Administration of antibiotics has been the most commonly applied remedy used for facing vibriosis outbreaks, giving rise to concerns about development and spreading of antibiotic resistant bacteria in the environment. Bacteriophage therapy, constitutes a potent alternative not only for treatment but also for prevention of vibriosis in aquaculture and the current thesis addresses the potential and challenges of using phages to control Vibrio pathogens. The combinatory administration of virulent bacteriophages φSt2 and φGrn1, isolated against Vibrio alginolyticus significantly reduced the Vibrio load in cultures of Artemia salina live prey, decreasing subsequently the risk of a vibriosis outbreak in the marine hatchery. During infection, the phages φSt2 and φGrn1 also hijack and reprogram the host metabolic machinery in order to meet their augmented demands for energy and nucleotide biosynthesis. Their lytic efficacy combined with their ability to manipulate the host’s energy production mechanisms, render them ideal candidates for phage therapy applications. Lytic phage vB_VspP_pVa5 that has been isolated against the rapidly emerging pathogen V. splendidus is also a promising candidate for phage therapy application according to its gene content and in vitro performance against its host. The genetic features of vB_VspP_pVa5 provide also a better insight to the evolution and genomic composition of the N4-like Vibriophages, a rather unexplored phage genus. Vibriophages are the natural predators of Vibrios responsible for shaping their communities in nature, however, only lytic phages obligately lead to the death of the bacterial host after infection; hence the whole phage therapy concept is relied on lytic phages. However, the wide presence of lysogeny in Vibrios dictates the high importance of temperate phages as well, primarily in driving bacterial evolution. Genetically similar Vibriophages, designated as H20-like phages, have been isolated against V. anguillarum as free phages and also identified as prophages in V. anguillarum genomes. Their widespread presence suggests a mutualistic interaction between this group of specific phages and their Vibrio hosts on a global scale. Current PhD thesis represents a multifaceted approach to studying the interactions between marine pathogenic Vibrio and their corresponding bacteriophages, while discussing the potential and limitations of phage therapy application in the biological control of vibriosis.