|Ph.D Student||Alperovitch Ariella|
|Subject||Photosystem I and II Genes in Marine Cyanophage Genomes|
|Department||Department of Biology||Supervisor||Professor Oded Beja|
|Full Thesis text|
Oceans cover more than 70% of the earth’s surface and play a vital role in the global carbon cycle. Unicellular cyanobacteria of the Synechococcus and Prochlorococcus genera are important contributors to primary production in the open oceans. Recently, core photosystem II (PSII) genes were identified in several marine cyanophages from the myovirus and podovirus families. These PSII genes were proposed to be functional and increase viral fitness by supplementing the host production of these proteins.
In this study, we show the first evidence of the presence of photosystem I (PSI) gene cassettes, in addition to PSII genes, and NADH dehydrogenase genes in cyanophage genomes. Using a combination of different marine metagenomic datasets, we show the presence of seven cyanobacterial core PSI genes, psaA, B, C, K, E, D, and a unique JF fusion gene. Potentially, these viral genes can encode to seven PSI proteins that are sufficient to form an intact monomeric PSI complex. Moreover, the presence of modified PSII and PSI genes in the same viral entities in combination with electron transfer proteins such as NAD(P)H dehydrogenate (NDH-1 complex) suggests a perturbation of the cyanobacterial host photosynthetic electron flow. Hence, depending on the physiological conditions of the infected host, the viruses may use different strategies to maximize survival. The modified PSI may alternate between functioning with PSII in linear electron chain transfer and contributing both NADPH and ATP levels, or functioning independently of PSII in the cyclic mode via the NDH-1 complex, and thus generating only ATP.
In order to characterize cyanophages carrying both photosystem genes in their genome, phage isolation was done using a phage sample from the Caroline Atoll in the Line Islands. PCR reactions confirmed the presence of both psaJF and psbA genes in the phage genome. In addition, transmission electron microscopy and the T4-like cyanomyrovirus g20 gene PCR reaction established the phage as a myovirus.