vB_PaeM_MiJ3: A Novel Jumbo Phage Infecting Pseudomonas aeruginosa Possesses Several Unusual Genomic Features. Phage Isolation

Phages are the most abundant biological entity on earth. There are many variants in phage virions size and morphology and genome sizes. Several large virion size phages with genome sizes greater than 200 kbp have been identified, and termed Jumbo phages. They exhibit several characteristics that are not typical for phages with smaller genomes. In this work, a rare jumbo phage named Mij3 (vB_PaeM_Mij3) capable of infecting Pseudomonas aeruginosa PAO1 strain was isolated from a horse farm in Leicestershire, United Kingdom. The phage was characterised biologically and genetically. Mij3 is a Myovirus with long multiple tail fibres. Host range of Mij3 revealed its ability to infect a variety of clinical isolates of P. aeruginosa. Bioinformatics analysis of the phage genome indicated that Mij3 is a novel phage. It possesses several unusual features that either rarely occur in other phages, or have not been reported in phages before. In particular, the phage encodes a FtsH-like protein and a putative lysidine synthase TilS, the two proteins that have not been observed in phages to date. Mij3 also possesses a split DNA polymerase B with a novel intein. Unlike other jumbo phages infecting Pseudomonas, Mij3 lack the phage nucleus and spindle which were believed to be conserved in all large Pseudomonas phages.