Cry11Aa toxin of Bacillus thuringiensis interactions with intracellular organelles in insect gut implicating actin depolymerization, massive endocytosis, and vesicle secretion.

Proteins with insecticidal activity from Bacillus thuringiensis are key factors in the process of bacterial pathogenesis. We examined the response of mosquito-larval midgut cells to Cry11Aa toxin. After Cry11Aa binding to specific membrane receptors, located in the brush border microvilli, pore formation activity of the toxin induced actin depolymerization and extensive endocytosis, followed by the secretion of large membrane vesicles into the lumen. These vesicles are segmented by endoplasmic reticulum membranes and actin, and contained damaged organelles (endosomes, lysosomes, mitochondria) but lacked DNA. The Cry11Aa toxin was also found in these vesicles, suggesting that vesicle secretion may be participating in a detoxification mechanism. Transmission electron microscopy confirmed the presence of these vesicles in the midgut lumen. Finally, Cry11Aa also invaded the cytoplasm of some midgut cells. Comparison with the non-toxic Cry11E97A mutant, defective in oligomerization and membrane insertion, confirmed the role of pore formation activity of Cry11Aa for triggering these processes. Here, we provide high-resolution images by using a novel image analysis strategy named Mean Shift Super Resolution (MSSR) microscopy, showing the cellular responses to this pore forming toxin, revealing conserved mechanisms across organisms and expanding our understanding of host interactions of this insecticidal protein during its mechanism of action.