| Summary: | Memoria de tesis doctoral presentada por Elena Lara de la Casa para optar al grado de Doctora por la Universidad de las Palmas de Gran Canaria (ULPGC), realizada bajo la dirección de la Dra. Dolors Vaqué Vidal del Institut de Ciències del Mar (ICM-CSIC) y de la Dra. Silvia G. Acinas.-- 274 pages [EN] There are an estimated 10 viruses in the world oceans, the majority of which are phages (viruses that infect bacteria). Extensive research has demonstrated the significant influence of marine phages on microbial abundance, community structure, genetic exchange and global biogeochemical cycles. In this thesis, we contribute to increase the knowledge about the ecological role of viruses in marine systems, but also we aimed to provide a better understanding about the interactions between phages and their hosts and the genetic pool and biogeography of some the isolated phages genomes. Firstly, we followed the seasonal variability of viral communities in a coastal marine site (Blanes Bay Microbial Observatory, BBMO) and the environmental and biological factors that could modulate them. Our results showed that viral communities did not follow any clear seasonal patterns during the 5 years studied period and that viruses were mainly negatively correlated with salinity. Secondly, given the actual concern of the climate change effects on marine ecosystems, we evaluated experimentally how increasing temperatures would affect the microbial loop via protists respect to via viruses (“viral shunt”) in two contrasting Arctic marine systems. Lytic life strategy dominated instead the lysogenic strategy when we increased the temperature. But, overall the most important factor controlling bacterial abundance was bacterivory. These two studies provide us a general overview regarding viral dynamics at the community level but without knowing who infects whom and who is doing what. To provide inputs into these relevant issues, we used the model of Pseudoalteromonas bacterial strains and its phages. Our results suggest that interactions ...
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