Study of the diversity in a group of phages of <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> species PB1 (Myoviridae) and their behavior in adsorbtion-resistant bacterial mutants

A group of 12 Pseudomonas aeruginosa virulent bacteriophages of different origin scored with regard to the plaque phenotype are assigned to PB1-like species based on the similarity in respect to morphology of particles and high DNA homology. Phages differ in restriction profile and the set of capsid major proteins. For the purpose of studying adsorption properties of these phages, 20 random spontaneous mutants of P. aeruginosa PAO1 with the disturbed adsorption placed in two groups were isolated. Mutants of the first group completely lost the ability to adsorb all phages of this species. It is assumed that their adsorption receptors are functionally inactive or lost at all, because the attempt to isolate phage mutants or detect natural phages of PB1 species capable of overcoming resistance of these bacteria failed. The second group includes five bacterial mutants resistant to the majority of phages belonging to species PB1. These mutants maintain the vigorous growth of phage SN and poor growth of phage 9/3, which forms turbid plaques with low efficiency of plating. In the background of weak growth, phage 9/3 yields plaques that grew well. The examination of the progeny of phage 9/3, which can grow on these bacteria, showed that its DNA differed from DNA of the original phage 9/3 by restriction profile and is identical to DNA of phage PB1 with regard to this trait. Data supported a suggestion that this phage variant resulted from recombination of phage 9/3 DNA with the locus of P. aeruginosa PAO1 genome encoding the bacteriocinogenic factor R. However, this variant of phage 9/3 did not manifest the ability to grow on phage-resistant mutants of the first group. Possible reasons for the difference between phages 9/3 or SN and the remaining phages of PB1 species are discussed. A preliminary formal scheme of the modular structure for adsorption receptors on the surface of P. aeruginosa PAO1 bacteria was constructed based on the analysis of growth of some other phage species on adsorption mutants of the first type.