טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentYotam Hulata
SubjectIsolation, Characterization and Annual Patterns of
Cyanophages in Lake Kinneret
DepartmentDepartment of Biology
Supervisor Professor Lindell Debbie
Full Thesis textFull thesis text - English Version


Abstract

Lake Kinneret is the largest upper natural source of freshwater in Israel. Cyanobacteria in the lake are composed of both unicellular and filamentous types and have predictable seasonal dynamics. However, no information exists about cyanophages nor how they affect cyanobacterial dynamics. In order to begin assessing the role of cyanophages in this system, we isolated and characterized cyanophages infecting both unicellular and filamentous cyanobacteria and assessed their abundances in Lake Kinneret over the year. The morphology of a phage infecting the non-endemic unicellular Synechococcus spp. was that of a cyanomyovirus with an icosahedral capsid and a contractile tail. The genome of this phage was 180 kb long with 220 open reading frames (ORFs). It contains structural and DNA replication genes homologous to T4 and thus belongs to the T4-like cyanophage family. Similar to marine cyanophages, it also has bacterial-like genes such as the photosystem II D1 protein and a high light inducible protein. A phage that infects Cylindrospermopsis raciborskii has an icosahedral capsid and a short tail. The C. raciborskii phage genome is 95 kb long and contains 107 ORFs. It has very few replication and structural genes recognized from known phages, indicating that it is a novel phage. This phage codes for some unusual bacterial-like genes, such as a cell division protein and a RNA polymerase sigma factor. However it lacks photosynthesis genes. In order to assess the abundance of these cyanophages in Lake Kinneret we used genomic information to design specific quantitative PCR primers. Quantification was done on water samples collected from Station A on a weekly basis from the depths of 1, 5, 15m during 2014. The abundance of the C. raciborskii phage changed over the year, as did its host, with low concentrations in winter and higher abundances during the spring and summer. The Synechococcus phage was under the limits of detection in the first half of the year but was abundant in the beginning of the summer and autumn. Strikingly, the patterns observed in both of the phages were similar for the 3 depths that represent the photic zone. This work provides the first insight into cyanophages and their dynamics in Lake Kinneret.