Abstract: Transposon mini-Tn5 was used to integrate Bt cryIA© gene into the chromosome of the biocontrol bacterium Pseudomonas fluorescens P303-1 by electroporation. Digestion analysis and PCR amplification of the chromosomal DNA demonstrated the existence of the cryIA© gene and strong vegetative promoter in the chromosome of these transformants. SDS-PAGE,ELISA analysis and transmission electron microscope observation verified the efficient expression of insecticidal crystal protein in P303-1 Bioassay results showed these engineered bacteria were strikingly insecticidal to cotton bollworms. The LC₅₀ of these bacteria against the second instar of cotton bollworms after five days was 50.1281 μg/g, 71.7763 μg/g, 69.0820 μg/g, 57.9895 μg/g, 192.8747 μg/g. Mortality of the treated larvae manifested a positive linear correlation with bacteria concentration,while weight showed a negative linear correlation with concentration.

Key words: transposon mini-Tn5, Pseudomonas fluorescens, Bt cryIA? gene, cotton bollworm