Genomic DNA of P. putida strains were extracted using an E.Z.N.A. Bacterial DNA kit (Omega Bio-tek Inc., USA), plasmids and PCR products were purified using a Gel/PCR DNA Fragment Extraction kit (IBI Scientific, Canada), and the DNA fragments from restriction endonuclease reactions were purified using an E.Z.N.A. MicroElute DNA Clean-Up kit (Omega Bio-tek Inc.) according to the protocol provided by the manufacturer.