INTEGRATION OF A PLASMID CARRYING THE attP SITE INTO THE CHROMOSOME OF RHIZOBIUM INSENSITIVE TO THE LYSOGENIC PHAGE INFECTION

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Fourteen strains belonging to the genera Rhizobium, Bradyrhizobium and Agrobacterium were investigated for susceptibility to infection by a lysogenic phage (phage φU) from Rhizobium leguminosarum biovar trifolii. All strains tested were resistant to phage φU infection; however, the phage was able to adsorb to R. leguminosarum biovar viciae strain K5. Plasmid pCI6 carrying the attachment site (attP) of phage φU was introduced into all these strains by conjugation. The tetracycline resistance (Tc^r) gene on pCI6 was used as a selectable marker. When R. leguminosarum biovar viciae strain K5 was used as a recipient, Tc^r transconjugants appeared at high frequency (4.41×10^-3). Southern hybridization with the attP fragment of phage φU indicates that pCI6 is integrated into the chromosome of 10 transconjugants. Furthermore, the restriction map of pCI6 integration region on the chromosome of strain K5 was shown to be identical to that of R. leguminosarum biovar trifolii strain 4S which was the original host strain of phage φU.