Transformation of pBR322-Derived Plasmids in Phytopathogenic Pseudomonas avenae and Enhanced Transformation in Its Proline-Auxotrophic Mutant

Efficient transformation of pBR322 and its derived plasmids, which have been widely used as cloning vectors in Escherichia coli, was observed in Pseudomonas avenae (K1), the pathogen of leaf blight disease in cereals. Moreover, there was a 10- to 50-fold transformation efficiency (1.3–3.0 × 10⁶/μg DNA) in the proline-auxotrophic mutant (Pr47), whose virulence to rice seedlings decreased. Similar enhancement of the frequency of transfer by mobilization of RSF1010, a broad host range plasmid, was observed in the recipient Pr47 strain in mating with donor Pseudomonas syringae. The plasmids harbored in these strains were maintained very stably after subcultures. Thus, a highly efficient transformation system with pBR322-derived plasmids used as a vector and Pseudomonas as a host bacterium was developed. Received: 13 July 1996 / Accepted: 26 August 1996