Ultrastructural Changes in Hemocyte Cells of Hard tick (Hyalomma dromedarii: Ixodidae): A model of Bacillus thuringiensis var. thuringiensis H14 delta-endotoxin mode of action

摘要

The ultrastruture and characteristics of hemocytes of ixodidae tick, Hyalomma dromedarii, after treatment with Bacillus thuringiensis serovar thuringiensis H14 8-endotoxin were studied. Little information is available on the systemic effects of Bacillus thuringiensis toxins in the hemocoel of arthropods. To evaluate the effect of B. thuringiensis 43-kDa toxins elicit a toxic response in the hemocoel, it was measured the effect of intrahemocoelic injections of 43-kDa Cry4Ba toxin on the hemocytes (ultrastructure and characteristics) and survival of Hyalomma dromedarii engorged female. It was found that of 43-kDa Cry4Ba toxin was highly toxic In short term (48h) to Hyalomma dromedarii engorged female, the resulte indicated that the complete growth wasarrest and death in a dose-dependent manner. On receiving 10mul of 157mug ml~(-1) soluble B. t. toxin/tick a rapid paralysis, followed by hemocytic disruption and death was occurred. This investigation revealed that a severe damage in the cells membraneand granulocytes of the hemolymph after injection with 8-endotoxin. Bacillus thuringiensis var. thuringiensis H14 8-endotoxin, this toxin destroys the granular cell and renders it abnormal. These cells are stored defensin and secreted it in hemolymph plasma after the exposure of the tick to bacterial infection. This explains the mechanism of action of this bacteria Bacillus thuringiensis on H. dromedarii hard tick. It kills the tick by causing a malfunction of the cellular immune system of the tick. The model proposed for Cry4Ba is that injected with toxins may reach a hemocytic target, as demonstrated by the good correlation between cytotoxicity and toxicity upon injection. In conclusion, the results of This study suggests that Bacillus thuringiensisvar. thuringiensis 8-endotoxins targets are not only present in the gut. This is an important result of biological relevance at the level of Bacillus thuringiensis mode of action.