Properties of natural interspecific hybrids of transposable phages of Pseudomonas aeruginosa: Specific features of phage PL24 transposition

Properties of natural hybrid transposable phages (TP) of Pseudomonas aerugi nosa, including phage PL24 and lysogens for this phage, were studied. PL24 possesses the properties of TP from two previously described groups, B3 and D3112. Its genome, unlike the genome of D3112, contains many sites suscept ible to the SalGI restriction endonuclease and possesses no more than 100 n ucleotides of bacterial origin located at the left genome end. However, unl ike B3, phage PL24 failed to induce auxotrophic mutants upon integration in the bacterial genome. This phage differed from both B3 and D3112 in sensit ivity to chloroform treatment. A more detailed examination of a group conta ining 25 randomly isolated lysogens for phage PL24 revealed previously unkn own processes occurring at early stages of bacterial lysogenization. There are at least two different modes of cell lysogenization with phage PL24. In the first case, the emerging lysogens contained a single prophage genome l ocated (in each lysogen) at individual sites. In the second case, polylysog enic bacteria appeared, and, after primary integration of a phage genome, r eplicative transposition occurred at new sites (often accompanied by the ap pearance of prophage clusters at these sites). The choice of the mode of ly sogenization can be determined both by differences in the physiological sta te of bacteria and by specific features of phage PL24, which possibly affec t the time of repressor accumulation to the concentration sufficient for bl ocking phage growth or the stability of the lysogenic state.