Genomic analysis of freshwater cyanophage Pf-WMP3 Infecting cyanobacterium Phormidium foveolarum: the conserved elements for a phage.

Cyanophages are ecologically abundant, genetically diverse in aquatic environments, and affect the population and evolutionary trajectories of their hosts. After reporting the cyanophage Pf-WMP4 genome (Liu et al. in Virology 366:28-39, 2007), we hereby present a related cyanophage, Pf-WMP3, which also infects the freshwater cyanobacterium Phormidium foveolarum. The Pf-WMP3 genome contains 43,249 bp with 234 bp direct terminal repeats. The overall genome organization and core genes of the two phages are comparable to those of the T7 supergroup phages. Compared with Pf-WMP4, cyanophage Pf-WMP3 has diverged extensively at the DNA level; however, they are closely related at the protein level and genome architecture. The left arm genes for the two phages, which mainly encode the DNA replication machinery, are not conserved in the gene order. Whereas the right arm genes of the two phages coding for structural proteins show high similarity in amino acid sequences and modular architecture, indicating that they have retained similar development strategies. The differences in similarity levels between the left and right arm genes suggest that the structural genes are the most conserved elements for a phage.