Characterization and Genomic Analysis of a Plaque Purified Strain of Cyanophage PP

Cyanophages are ubiquitous and essential components of the aquatic environment and play an important role in the termination of algal blooms. As such, they have attracted widespread interest. PP was the first isolated cyanophage in China, which infects Plectonema boryanum and Phormidium foveolarum. In this study, this cyanophage was purified three times by a double-agar overlay plaque assay and characterized. Its genome was extracted, totally sequenced and analyzed. Electron microscopy revealed a particle with an icosahedral head connected to a short stubby tail. Bioassays showed that PP was quite virulent. The genome of PP is a 42,480 base pair （bp）, linear, double-stranded DNA molecule with 222 bp terminal repeats. It has high similarity with the known Pf-WMP3 sequence. It contains 41 open reading frames （ORFs）, 17 of which were annotated. Intriguingly, the genome can be divided into two completely different parts, which differ both in orientation and function.