New Bacillus thuringiensis toxin combinations for biological control of lepidopteran larvae

Cyt1Aa from Bacillus thuringiensis israelensis is known by its synergistical activity with B. thuringiensis and Bacillus sphaericus toxins. It is able to improve dipteran specific toxins activity and can prevent or overcome larval resistance to those proteins. The objective of the current study was to investigate the possible improvement of larvicidal activity of B. thuringiensis kurstaki expressing heterogeneous proteins Cyt1A and P20. cyt1A98 and p20 genes encoding the cytolytic protein (Cyt1A98) and the accessory protein (P20), respectively, were introduced individually and in combination into B. thuringiensis kurstaki strain BNS3. Immunoblot analysis evidenced the expression of these genes in the recombinant strains and hinted that P20 acts as molecular chaperone protecting Cyt1A98 from proteolytic attack in BNS3. The toxicities of recombinant strains were studied and revealed that BNS3pHTp20 exhibited higher activity than that of the negative control (BNS3pHTBlue) toward Ephestia kuehniella, but not toward Spodoptera littoralis. When expressed in combination with P20, Cyt1A98 enhanced BNS3 activity against E. kuehniella and S. littoralis. Thus, Cyt1Aa protein could enhance lepidopteran Cry insecticidal activity and would prevent larval resistance to the most commercialized B. thuringiensis kurstaki toxins.