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Abstract

In order to reduce the use of chemical pesticides, organic farming are using biopesticides.
Bacillus thuringiensis var kurstaki (Btk) is the most used biopesticide around the world. Btk is a Gram positive soil bacterium. When resources are limited, vegetative Bt cells undergo sporulation, synthesizing a protein crystal during spore formation. Proteins in these crystals are called Cry endotoxins and have been known for decades to display insecticidal activity against specific insect groups by destroying their gut and leading to their death by septicemia.
My PhD project aims to study the impacts of Btk on the gut homeostasis of non-target organisms. For that, I will use the powerful laboratory model Drosophila melanogaster.
In the Drosophila midgut, Intestinal Stem Cells (ISCs) are required for maintenance of the proper cell composition in the adult intestine. To ensure permanent recruitment of newly differentiated cells, ISCs undergoe asymmetric cell division that generates an ISC itself and a progenitor cell. Then, the level of Notch pathway activation in progenitor cells will commit them toward enterocytes (at high Notch activation) or enteroendocrine cells (at low Notch activation) differentiation. Upon a bacterial intoxication that causes gut damages, intestinal cell renewing is accelerated and most of progenitor cells differentiate into enterocytes to replenish the damaged ones.
Strikingly, our work revealed that the number of enteroendocrine cells (EEC) increases after an intoxication by the commercialized form of Btk despite the damages caused to the enterocytes. We have shown that this EEC increase is dependent on the Cry toxins.
My work is to understand how Btk induces an increase in EECs at the expense of enterocyte differentiation and the putative link between Cry toxins and the inhibition of Notch pathway. 

Key-words

Bioinsecticides, Bacillus thuringiensis (Bt), Drosophila melanogaster, intestinal homeostasis , Cry toxins , Notch pathway .