Interaction of bacteriophage P1 with an epiphytic strain-the role of the interplay between various mobilome elements.

P1 is a model, temperate bacteriophage of the 94 kb genome. It can lysogenize representatives of the order. In lysogens, it is maintained as a plasmid. We tested P1 interactions with the biocontrol L15 strain to explore the utility of P1 in genome engineering. A P1 derivative carrying the Tn (cm) transposon could transfer a plasmid from to the L15 cells. The L15 cells infected with this derivative formed chloramphenicol-resistant colonies. They could grow in a liquid medium with chloramphenicol after adaptation and did not contain prophage P1 but the chromosomally inserted cm marker of P1 Tn (). The insertions were accompanied by various rearrangements upstream of the Tn gene promoter and the loss of IS (ISL) from the corresponding region. Sequence analysis of the L15 strain genome revealed a chromosome and three plasmids of 0.58, 0.18, and 0.07 Mb. The largest and the smallest plasmid appeared to encode partition and replication incompatibility determinants similar to those of prophage P1, respectively. In the L15 derivatives cured of the largest plasmid, P1 with Tn could not replace the smallest plasmid even if selected. However, it could replace the smallest and the largest plasmid of L15 if its Tn ISL sequence driving the Tn mobility was inactivated or if it was enriched with an immobile kanamycin resistance marker. Moreover, it could develop lytically in the L15 derivatives cured of both these plasmids. Clearly, under conditions of selection for P1, the mobility of the P1 selective marker determines whether or not the incoming P1 can outcompete the incompatible L15 resident plasmids. Our results demonstrate that can serve as a host for bacteriophage P1 and can be engineered with the help of this phage. They also provide an example of how antibiotics can modify the outcome of horizontal gene transfer in natural environments. Numerous plasmids of strains appear to contain determinants of replication or partition incompatibility with P1. Therefore, P1 with an immobile selective marker may be a tool of choice in curing these strains from the respective plasmids to facilitate their functional analysis.