Genes and Structural Proteins of the Phage Syn5 of the Marine Cyanobacteria, Synechococcus

Welkin H. Pope, Ph.D., 2005
Jonathan King, Advisor

Bacteriophage have been proposed to be the most abundant organisms on the planet, at an estimated 1031 particles globally. Bacteriophage tails determine host specificity and provide the mechanism of passage of the phage genome into the host cell.
Marine cyanobacteria of the genera Prochlorococcus and Synechococcus are numerically dominant photosynthetic cells in the open oceans. Few studies have examined the structural proteins of the phages of these genera, termed "cyanophage".

Cyanophage Syn5 is a short-tailed phage which infects Synechococcus strain WH8109. Methods of concentrating the phage to 1012 particles/ml by PEG precipitation were developed. The burst size of Syn5 was 30 phage/cell and its lytic period was 10 hours.
Sequencing of the Syn5 genome revealed a genome length of 46,214 bp with a 237bp terminal repeat. Annotation of the genome identified 61 ORFs, and revealed a relationship to the phages T7, P-SSP7, and P60. Syn5 possessed an extensive DNA replisome and lacked photosynthetic genes.

The structural proteins of Syn5 were characterized by mass-spectroscopy and N-terminal sequencing. Eleven protein chains were identified, including portal, capsid, tail tubes, and internal proteins; most with similar copy numbers to T7. Three unidentifiable proteins were found in the particle; two were antigenic, as demonstrated by Western blot. Characterization of these proteins may provide insight to the host recognition abilities of cyanophages.