We have constructed a high-copy-number, broad-host-range plasmid, pMEFE1 that carries a gene encoding an ethylene-forming enzyme from Pseudomonas syringae pv. phaseolicola PK2. The ethylene-forming enzyme was expressed under the control of a promoter of the neomycin phosphotransferase gene on pMEFE1. When introduced into P. syringae and Pseudomonas putida cells by transconjugation, pMEFE1 conferred on the recombinant cells the ability to synthesize the ethylene-forming enzyme with specific activities 41 and 20 times higher, respectively, than that of the ethylene-forming enzyme in the parental P. syringae.