|M.Sc Student||Shamir Nitzan|
|Subject||Population Dynamics of T7-Like Cyanophages During|
the Spring Bloom in the Gulf of Aqaba
|Department||Department of Biology||Supervisor||Professor Debbie Lindell|
|Full Thesis text|
Marine cyanobacteria of the genera Synechococcus and Prochlorococcus are important primary producers in the world ocean. Cyanophages, viruses that infect cyanobacteria, are one of the factors that control their population size. T7-like cyanophages are a major component of the cyanophage community and there are two distinct clades within them, A and B, which have different biological properties and environmental abundances. T7-like cyanophages can now be quantified using the polony method. In the Gulf of Aqaba, Synechococcus and Prochlorococcus undergo seasonal succession. Synechococcus blooms when the water column begins to stratify in the spring, and Prochlorococcus becomes numerically dominant when stratification is fully established at the end of spring. This research project aims to investigate the dynamics of T7-like cyanophages during the spring period of 2015 and 2016 in the Gulf of Aqaba by measuring their abundance using the polony method. T7-like clade B cyanophages were more abundant than clade A cyanophages throughout the two sampling periods at all depths. Clade B phage abundance was positively correlated with Synechococcus abundance over the whole sampling period with a stronger correlation during the Synechococcus bloom. This correlation suggests that infection by clade B phages may not be the main factor that terminates the Synechococcus bloom. At the end of the spring, the integrated numbers of Prochlorococcus in the water column increased and the integrated numbers of clade B phages followed them with a week-long lag. It is possible that the composition of the clade B phage population changes from Synechococcus?-infecting to Prochlorococcus-infecting when the latter becomes more abundant. Clade A phages were weakly correlated with Prochlorococcus during the Synechococcus bloom, whereas they weren’t correlated with Synechococcus. This suggests that clade A phages that infect Prochlorococcus are more abundant than what was previously thought. This research project provides the first observations on T7-like phage dynamics on a near weekly time resolution. The data presented here do not provide support for the hypothesis that T7-like phages are the main cause of cyanobacteria mortality in the Gulf of Aqaba during the spring period. These data also emphasizes the need to directly investigate infection percentages using the polony method to better understand cyanobacteria-cyanophages interactions in the ocean.