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A novel, previously unknown cip gene of Pseudomonas aeruginosa phage D3112 was discovered. The cip gene is responsible for inhibiting the intracellular growth of the related heteroimmune phage B39 of P. aeruginosa. It was shown that the cip gene product inhibits replication of the B39 genome, interacting, apparently, with the definite s+ site in the phage B39 genome. Mutants cip- of phage D3112, incapable of inhibiting the growth of phage B39, and B39 mutants, insensitive to the action of the cip gene product of phage D3112, were isolated.

Mutants and recombinants of transposable Pseudomonas aeruginosa bacteriophage B39 with a specific phenotype Pde- (pleiotropic developmental effect) were studied. Pde- phages produce clear minute plaques on lawns of P. aeruginosa PAO1 and fail to grow in cells of PAO1 harbouring Rms 163 (Inc P5) plasmid. Pde+ character is under control of the two loci in phage genome which were designated pdeX and pdeY. In hybrid phages the pdeX and pdeY loci originating from different transposable phages (pdeX from B39 and pdeY from PH132) do not accomplish their function and, as a result, the hybrid phages have the Pde- phenotype. The frequency of integration (f.o.i.) of Pde- phages into bacterial chromosome is lower than f.o.i. for Pde+ phages, as well as the frequency of stable lysogenization of infected bacteria; lytic development of the Pde- phages is also limited. The great difference among the transposable phages in their reaction to the presence of Rms163 plasmid is caused by some differences in the specific rms site in the phage genome. The site is located inside the interval 1.1-3.9 kb of the physical genome map, being closely linked to cI gene of phage B39. The growth of Pde- phages in cells with Rms163 can be restored, due to additional mutations in phage genes affecting lysogenization.

Bacterial cells lysogenic for D3112, a transposable Pseudomonas aeruginosa phage restrict the growth of a related heteroimmune B39 phage. The lysogens are divided into two different types PAO(D3112). In the lysogens of the type I the efficiency of B39 growth only decreases slightly, the lysogens of the type II restricting completely the growth of this phage (e.o.p. is less than 10(-7). As shown by the results of Southern hybridization experiments, lysogens of the type I are monolysogens, while those of the type II are double or polylysogens. Restriction of B39 in PAO(D3112) is caused by expression of a locus in the D3112 genome. The locus has been termed as cip (control of interaction of phages). The cip locus was mapped at the interval 1.3-2.45 kb of the D3112 physical map using different deletion derivatives of D3112. Expression of cip only takes place in the prophage state and not during the phage lytic development. When expressed, cip affects the early steps in the growth of B39 lowering the level of integration and transposition processes; the effect is not dependent on the way of initiation of the lytic cycle (through prophage induction or infection).

Using a large group of newly isolated deletion mutants of prophage D3112 the location of all known mutations of D3112 phage was more precisely defined. The mutations affecting establishment of lysogenic state were mapped in two regions of the genome- 0-1.3 and 29-30 kb. The replicative A gene is mapped between 1.3 and 4.9 kb, the second replicative B gene being situated on the right of the A gene, between 4.9 and 9.4 kb. The C gene which is responsible for positive regulation of phage late genes' expression is mapped within the 9-12 kb region. It is suggested that promoter of the gene C is situated within the same interval. Mutations were isolated in the Lys gene which is responsible for host cell lysis. The gene is located within the interval 14-22 kb of the physical map. The order of morphogenetic genes in the late genome region was also established.

The influence of Rms163 plasmid on lysogenization of Pseudomonas aeruginosa cells by B39 phage was studied. Plasmid Rms163 was shown to increase the frequency of lysogenization of PAO1 cells 7-8 times. C-mutants of B39 phage were isolated. According to complementation test, c-mutants were distributed into two groups--cI and cII/III. The product of cI is essential for establishment and maintenance of lysogenic state, cII/cIII product being only necessary for establishment of lysogenization. The mutants with special characteristics were isolated: B39cx1 phage carries a mutation which seems to be located on a regulatory site essential for establishment of lysogenic state. The region of the B39 genome responsible for interaction with Rms163 plasmid was mapped. Possible mechanisms of Rms163 plasmid interference with transposable B39 phage are discussed.