|M.Sc Student||Schwartz Daniel|
|Subject||Generalized Transduction in Marine Cyanobacteria|
|Department||Department of Biology||Supervisor||Professor Debbie Lindell|
|Full Thesis text|
The influence horizontal gene transfer (HGT) has on the evolution of bacteria is now widely accepted as it is well documented in their genomes. Though the mechanisms of HGT are well known and have been employed extensively as genetic tools, the evolutionary research of HGT has focused mainly on the processes’ end products (extant genomes) and little is known regarding the importance and contribution of the different modes of HGT - transformation, conjugation and transduction. Genomic data suggests that HGT is one of the major processes shaping the diversity of the globally widespread marine picocyanobacteria of the genera Synechococcus and Prochlorococcus, and that viruses (cyanophages) play a central role as both vectors and as donors and recipients in these transfers. Yet, the mechanisms underlying genetic transfer among these organisms remain obscure as hardly any experimental studies have addressed this topic. This work aimed to provide insight into the evolution of marine picocyanobacteria by developing a quantitative generalized transduction system in which cyanophages could be tested for their ability to transfer a genetic marker between strains of Synechococcus and Prochlorococcus. Such a system could also supply the basis for the development of a long needed genetic manipulation system for Prochlorococcus. To this end a genetic marker was optimized to better resemble cyanobacterial native genes and a set of broad host-range cyanophages were isolated and characterized. The generalized transduction system developed here was used to test the transfer of antibiotic resistance marker genes carried either on a plasmid or integrated in the chromosome by a variety of cyanophages between lines of Synechococcus sp. WH8102 and from it to other strains of picocyanobacteria. No transduction was observed in any of the experiments. These results may suggest that generalized transduction is not a widespread mode of HGT among picocyanobacteria. Alternatively it is possible that transduction is carried out by these cyanophages but at a frequency lower than the systems’ detection limit, or that secondary lytic infection of transduced cyanobacteria has prevented the detection of transduction. The data at hand currently does not enable to differentiate between these two explanations. A parallel attempt made to quantify cyanophage encapsidation of host DNA, which could serve as a screening method for possible transducing cyanophages, did not yield results mainly due to as yet unresolved difficulties in the isolation and quantification cyanophage DNA.