We present a jumbo Pseudomonas bacteriophage, PA5oct, which represents a novel genus of bacterial viruses. The virion morphology and genome analysis indicates that this myovirus differs from all known giant phages. PA5oct has a head of about 131 nm in diameter and a tail of 136 x 19 nm. It has a giant linear A+T-rich (33.3% GC) double-stranded DNA genome (287 182 bp), making it the third largest sequenced Pseudomonas phage genome and the eight jumbo genome among Myoviridae phages. Based on DNA sequencing 397 genes were predicted. Additional RNA sequencing allowed to identify another 65 genes (+14.1%) and confirm presence of previously predicted genes. Moreover, with this powerful tool the reads originating from the phage and the host at each stage of infection were mapped to the phage and host genomes respectively, revealing that PA5oct progressively dominates host transcription. Indeed PA5oct transcripts represented 21% of total transcripts within 5 minutes and eventually proceed to 69% then 92% by middle and late infection respectively. Further, based on bioinformatics and ESI-MS/MS analysis function was assigned to 123 genes (26.62% of all proteins), including 73 structural proteins (15.8% of all proteins).
To better represent genetic relationships between PA5oct and sequenced viruses, a gene-sharing network was built. In the network comprising 1,355 genomes, PA5oct showed weak connections to member viruses belonging to the Tevenvirinae in terms of shared gene contents. Notably, a network-based partitioning revealed that PA5oct is most closely related to a recently emerged new subfamily including Escherichia phages 121Q/PBECO 4, Enterobacteria phage vB_KleM-RaK2, Klebsiella phage K64-1, and Cronobacter phage vB_CsaM_GAP32, which indicates its genetic divergence as distant relatives of the T4 superfamily.