EXPRESSION AND INSECTICIDAL CHARACTERIZATION OF Cry8Db PROTEIN AGAINST Lepidiota signata Fabricius

Bacillus thuringiensis (Bt) is a ubiquitous Gram-positive bacterium that can produce different insecticidal proteins during the sporulation phase growth. The objective of this study was to examine the expression, including the effects of induction temperature, time and IPTG concentrations as well as investigate insecticidal activity of Cry8Db protein against Lepidiota signata Fabricious. The results showed that the cry8Db gene was expressed in Rosetta–gamy Escherichia coli strain at optimal temperature 28°C, 100 μM IPTG and for 4 h induction. SDS-PAGE and Western blot were applied to confirm the normal expression and transcription of the cry8Db gene which produced the polypeptide with a molecular mass of 73 kDa. Three stages of Lepidiota signata Fabricius larvae were examined in the bioassay to investigate their survival after 15 days. The protein exhibited high toxicity against Lepidiota signata Fabriciusin the three different larvae stages at the lowest mean lethal concentration of LC50 =183.7 ng/mL, 270.8 ng/mL and 345.5 ng/mL, respectively. This is the first report demonstrating Cry8Db protein against Lepidiota signata Fabricius larvae. The Cry8Db protein may become a potential environmentally friendly marker for the biological management of Lepidiota signata Fabricius.