Comparison of new giant bacteriophages OBP and Lu11 of soil pseudomonads with bacteriophages of the ?KZ-supergroup of Pseudomonas aeruginosa

Study of two recently isolated giant bacteriophages Lu11 and OBP that are active on Pseudomonas putida var. Manila and Pseudomonas fluorescens, respectively, demonstrated their similarity in morphotype, genome size, and size of phage particles, with giant bacteriophages of Pseudomonas aeruginosa assigned to the supergroup of ?KZ-like phages of the family Myoviridae. This supergroup was designated in this manner according to the best studied phage ?KZ that belongs to the species of this group widely distributed in nature. Comparison of major polypeptide sizes of mature particles suggests similarity of certain proteins in the phages examined. In OBP particles visualized with an electron microscope, an “inner body” was detected, which points to specific DNA package intrinsic to phages of ?KZ group. In the meantime, phages Lu11 and OBP do not exhibit resemblance among themselves or with any of earlier described ?KZ-like phages in respect to detectable DNA homology. Note that phage Lu11 of P. putida var. Manila exhibits very slight homology with phage Lin68 of the family of P. aeruginosa ?KZ-like phages detected only in blot hybridization. This suggests the possible involvement of these phages in interspecies recombination (“gene shuffling”) between phages of various bacterial species. Results of partial sequencing of phage genomes confirmed the phylogenetic relatedness of phage OBP to phages of the ?KZ supergroup, whereas phage Lu11 most probably belongs to a novel species that is not a member of supergroup ?KZ composition. The results of the study are discussed in terms of the evolution of these phages.