טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentHagay Enav
SubjectViral Adaptation to Different Hosts in the Marine
Environment
DepartmentDepartment of Biology
Supervisors Full Professor Beja Oded
Full Professor Mandel-Gutfreun Yael
Full Thesis textFull thesis text - English Version


Abstract

Marine viruses infect Bacteria, Archaea and Eukaryotic organisms and have a huge impact on the ecology and physiology of their hosts. In order to multiply, viruses need to use the host machinery. In order to maximize their reproductive potential, viruses need to adapt both to their hosts and to the extracellular environment. In this study we investigated two examples for the adaptation of marine viruses to their hosts.   

In the first project, we studied viruses infecting marine cyanobacteria of the genera Prochlorococcus and Synechococcus. These are the most abundant photosynthetic prokaryotes in oceanic environments, and are key contributors to global CO2 fixation, chlorophyll biomass and primary production. Cyanophages, viruses infecting cyanobacteria, contribute greatly to cyanobacterial mortality, therefore acting as a powerful selective force upon their hosts. Phage reproduction is based on utilization of the host translation mechanisms; therefore, differences in the G genomic content between cyanophages and their hosts could be a limiting factor for the translation of cyanophage genes. On the basis of comprehensive genomic analyses conducted in this study, we suggest that cyanophages of the Myoviridae family, which can infect both Prochlorococcus and Synechococcus, overcome this limitation by carrying additional sets of tRNAs in their genomes accommodating AT-rich codons. Whereas the tRNA genes are less needed when infecting their Prochlorococcus hosts, which possess a similar G content to the cyanophage, the additional tRNAs may increase the overall translational efficiency of their genes when infecting a Synechococcus host (with high G content), therefore potentially enabling the infection of multiple hosts.

In the second project we studied auxiliary genes (metabolic genes that were acquired from host genomes) enriched in marine viromes. While many individual auxiliary genes were observed in viral genomes and metagenomes, there is great importance in investigating the abundance of auxiliary genes and metabolic functions in the marine environment towards a better understanding of their role in promoting viral reproduction.

To identify enriched auxiliary genes, we analyzed marine viral metagenomes. Enriched genes were mapped to a “global metabolism network” that comprises all KEGG metabolic pathways. Our analysis of the viral-enriched pathways revealed that purine and pyrimidine metabolism pathways are among the most enriched pathways. Moreover, many other viral-enriched metabolic pathways were found to be closely associated with the purine and pyrimidine metabolism pathways. Our analyses strongly support the well-established notion that viral auxiliary genes promote viral replication via both degradation of host DNA and RNA as well as a shift of the host metabolism towards nucleotide biosynthesis