Effects of the P20 protein from Bacillus thuringiensis israelensis on insecticidal crystal protein Cry4Ba.

The accessory protein P20 from Bacillus thuringiensis israelensis has been defined as an important molecular chaperone for forming crystal Cyt1Aa, and enhancing Cry11Aa and Cry4Aa expression. To investigate its putative role in Cry4Ba delta-endotoxin production and toxicity, a p20 gene was cloned and introduced into B. thuringiensis recombinant strain expressing cry4Ba type gene (cry4BLB). The delta-endotoxin synthesis was enhanced by 262%. The generated inclusions were assayed against third instar larvae of Aedes aegypti. The combination of P20 protein with Cry4BLB delta-endotoxin led to a stable mortality rate of 25% with doses ranging from 0.2 mg l(-1) to 0.6 mg l(-1). Cry4BLB crystals produced in the presence of P20 were much less soluble than those produced by the control strain lacking P20 at pH lower than or equal to 10.5. The observed toxicity perturbation correlates with a decrease of Cry4BLB inclusions solubility. The presence of P20 protein has affected Cry4BLB crystallization and altered greatly its solubility properties. Cry4Ba effectiveness against A. aegypti larvae is related to the solubilization step in larval guts environment.