Characterization of a new Bacillus thuringiensis endotoxin, Cry47Aa, from strains that are toxic to the Australian sheep blowfly, Lucilia cuprina

Sixteen isolates of Bacillus thuringiensis, derived from various soil samples collected in Australia, are highly toxic to larvae of the sheep blowfly (Lucilia cuprina). The toxin gene from one of the strains (CAA890) was cloned by genome walking, and sequencing of the cloned fragments revealed a new cry gene, encoding a protein of 1134 amino acid residues, with a theoretical molecular mass of 139,209 Da. Based on the amino acid sequence comparison with known Cry δ-endotoxins, the gene was designated cry47Aa. Homology modelling based on known crystal structures of the Cry toxins reveals the differences to be located in the loops of domain II in the putative toxin-receptor binding surfaces between Cry47Aa and the dipteran active Cry2Aa. We also showed that the cry47Aa gene is present in the other isolates that are highly toxic to the sheep blowfly.