BEHAVIOR OF PLASMID PJB5JI IN RHIZOBIUM-HUAKUII UNDER FREE-LIVING ANDSYMBIOTIC CONDITIONS

The Rhizobium leguminosarum biovar viceae host-range plasmid pJB5JI wa s transferred into Rhizobium huakuii strains, both wild-type 7653R and its sym plasmid-cured mutant 7653R-1. Transconjugant 7653R-1 (pJB5JI) acquired the ability to form ineffective nodules on pea plants, where as transconjugant 7653R (pJB5JI) could not do so, indicating that the indigenous symbiotic plasmid could restrict the functional expression of pJB5JI. On the other hand, transconjugant 7653R (pJB5JI) showed hig her nitrogenase activity on A. sinicus and higher shoot dry weight tha n the recipient strain 7653R. The alien plasmid pJB5JI in both kinds o f transconjugants remained stable during frequent transfer on culture media, but in part of the isolates from nodules formed by them the pJB 5JI was not visualized on gel by the Eckhardt procedure Southern hybri dization with Tn5 and nod gene probes showed that these isolates still reserved, at least in part, DNA of pJB5JI, which was probably integra ted onto the chromosome of cells.