ORIGIN AND CHARACTERISTICS OF PSEUDOMONAS -AERUGINOSA PAO1 CLONES SURVIVING AFTER THE INDUCTION OF TRANSPOSABLE PROPHAGES

Various mutations cancelling the lethal effect of phage lytic developm ent and simultaneous phenotypic modifications were found in rare clone s surviving after incubation at 42 degrees C of Pseudomonas aeruginosa (D3112 cts 15), lysogenic for thermoinducible mutant cts 15 of the tr ansposable prophage (TP) D3112. All mutations arose prior to thermal i nduction. Temperature induction of other bacteriophages (nontransposab le) did not lead to selection of bacterial morphological mutants. Ther efore, it was concluded that mutagenesis occurred upon the partial (re versible) TP derepression accompanied by coupled replication-transposi tion of TP, the latter being the direct cause of the mutator effect. I solation of the P. aeruginosa PAO1 mutant R10 (this mutant is resistan t to infection with TP at 42 degrees C) allowed the proper selection a nd examination of numerous survivors. Comparison of their types derive d from lysogens with different prophage location indicated that the nu mber of secondary sites where TP integration is possible without the l oss of cell viability is limited. Several transposition events occurre d in the history of some survivors (during a repeated or single derepr ession event). Type D clones, which produce small colonies, are of spe cial interest, because mechanisms underlying the survival of such clon es are extremely diverse, and their phenotypes indicate the possibilit y of stable chromosomal rearrangements in the genome of P. aeruginosa.