MUTUAL ADAPTATION OF BACTERIOPHAGE-FD, PFD PLASMIDS AND THEIR HOST STRAINS

The synthetic plasmid pfdC1 with the replication origin of phage fd an d fd gene 2 grows autonomously in E. coli cells. DNA sequencing reveal ed several mutations compared to the fd genome causing reduced express ion of viral gene 2 protein, which can be toxic for the host cell. Ano ther adaptation was noticed for E. coli strains with a copy of fd gene 2 on the F-episome and a pfdA-plasmid with a minimal fd replication o rigin, when maintained at 42 degrees C. The carrier cells adjusted the ir cellular metabolism to these stress conditions, whereas replication functions of the plasmid or expression of fd gene 2 on the F-episome were not changed. The filamentous bacteriophages tend to reduce their genome size into miniphages, which was also observed for phages with a n antibiotic resistance gene. Bacteriophages with a transposon inserti on in the viral gene 2 had a tendency to restore the mutated gene by e xchange with the functional gene 2 carried in recA-host cells. Mobiliz ation of pfd-plasmids with RP4 transfer functions was reduced due to i nterference of replication and transfer in the rolling circle mode. Th e vectors used in these studies can also be applied as cloning vectors , which are compatible with many other plasmid vectors.