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Distribution and diversity of vibrio parahaemolyticus viruses (VpVs) and their hosts Comeau, Andreé Marcel

Abstract

Vibrio parahaemolyticus viruses (VpVs) and their hosts were used as model organisms to explore the distribution and diversity of single-species populations in multiple habitats of coastal British Columbia. Abundances of host and virus were first monitored for a year in oysters. Temporal changes in host-range patterns, derived from bacterial and viral isolates, demonstrated that a significant shift in virus strains occurred during the winter months. Calculations of virus-induced mortality indicated that the presence of additional host species may be required to sustain viral production during summer. During winter, the persistent VpV population also required bacteria other than the host species and/or cells of altered culturability. Secondly, the distribution, phage-typing patterns, and genetic diversity of V. parahaemolyticus and total Vibrio spp. were examined in the water column and sediments. The bacteria were widespread and, not surprisingly therefore, geographic distribution was a poor determinant of strain diversity. Environment of isolation however, had a much more profound effect on genetic diversity and on phage-typing patterns to an even greater extent. Sources of high abundance produced strains with high susceptibility to viral infection; and the opposite was true for the water column. Thirdly, random amplification of polymorphic DNA was modified using a degenerate primer to produce unique and reproducible banding patterns from viral genomes. The findings described a rapid, PCR-based tool (DP-RAPD) for strain-typing viral isolates that allowed inferences to be made on genetic relatedness within groups of related viruses. Finally, the DP-RAPD was used in an investigation that examined the spatial variation in hostrange and genetic diversity of newly isolated and characterized VpVs from the water column. VpVs were a nearly ubiquitous component of the water-column virioplankton, yet at very low abundances. When compared to oyster VpVs, it was clear that the major determinant of diversity was not geography, but the source habitat. Viruses from some of the farthest separated locations were closely related, while the diversity within some locations was very high. Overall, the diversity of viruses infecting a single Vibrio species was high and the host-virus populations were under similar phenotypic and genotypic selective pressures, mediated by the source habitat.

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