|M.Sc Student||Eyal Greengrass|
|Subject||Resistance of Marine Synechococcus to Podovirus|
Infection: Genetic Basis and Phenotypic
|Department||Department of Biology||Supervisor||Professor Lindell Debbie|
|Full Thesis text|
Cyanobacteria of the genus Synechococcus are widespread in the oceans as are the podoviruses that infect them. Their co-occurrence in nature suggests that resistant cells live among susceptible cells, but how resistance to podoviruses affects the genome and the phenotype of Synechococcus has yet to be explored. The aims of this research were to determine which host genes are under virus selection, to assess how resistance affects the phenotype of the host, and to test if there is any phenotypic or genotypic difference between resistance to 2 T7-like podoviruses belonging to different clades. To this end 35 substrains of Synechococcus WH8109 resistant to 2 podoviruses - S-TIP37 or Syn5 - were isolated. Whole genome sequencing of the resistant substrains was carried out and cross resistance and growth rate tests were performed. Genome analysis revealed that mutations conferring resistance converged at 2 paralogous porin-like genes; porinP and somB. Porins are membrane proteins which serve as a channel that transports nutrients, sugars or amino acids from the extracellular medium across the outer membrane to the periplasm of the cell. Twenty-four substrains had mutations in either or both porin-like genes as well as in other genes, while 5 substrains had only a single mutation. Two of these substrains had mutations in somB, one in porinP and the other two substrains had mutations in two hypothetical genes. The remaining 6 substrains had mutations in multiple genes other than porin genes. Three substrains appeared to have a much slower growth rate than the WT, implying that these substrains paid a fitness cost for their resistance. Cross-resistance tests showed that resistant substrains selected with S-TIP37 were resistant to Syn5 and vice versa, but not to another podovirus or to the 4 myoviruses tested. These findings suggest that these porin-like genes play a key role in the infection of Synechococcus WH8109 by both podoviruses despite their belonging to different lineages.