Histopathological and combinatorial effects of the metalloprotease InhA1 and Cry proteins of Bacillus thuringiensis against Spodoptera littoralis

The zinc metalloprotease (InhA) of Bacillus thuringiensis specifically hydrolyzes cecropins and attacins, two antibacterial peptides in the immune hemolymph of insects, leading to a high resistance of the bacteria to the humoral defense system of its host. In the present study, the inhA gene of B. thuringiensis strain BUPM28 was cloned and the nucleotide sequence analysis revealed that it was identical to that of B. thuringiensis 8010. The expressed InhA1 protein in Escherichia coli showed toxicity to neonate Spodoptera littoralis larvae with a LC50 of 2.07 ± 0.72 μg/cm2. Study of the effect of combining Cry proteins with InhA1 showed that one improves the toxicity of the other one against S. littoralis. Investigation of the histopathological effect of this metalloprotease showed an extensive damage of S. littoralis epithelium tissue. These results provide an insight to the use of InhA as supplement to Cry toxins to improve the efficacy of B. thuringiensis formulations and to overcome possible resistance problems.