engleski

The role of microbes as mediators of immune memory in insects

This thesis is composed in three individual studies focusing on the role of microbes in insect immunity, especially in the context of oral immune priming. In Chapter I we examined the role of microbes in oral priming in T. castaneum as an immune response to infections with B. thuringiensis. The main aim of the study was to further elucidate the mechanisms behind the already observed phenomenon of oral priming. As microbiotas have been suggested to shape immunological responses of their hosts, our hypothesis was that the eradication of commensal bacteria from the T. castaneum larvae might lead to the loss of the priming effect. In Chapter II we characterized important aspects of the infection of T. castaneum with entomopathogenic B. thuringiensis. The main aim of the study was to expand the knowledge about the host-pathogen interactions in our system. More specifically, we quantified the number of spores ingested by larvae which survived or died after the exposure to B. thuringiensis spores and Cry toxins ; we examined whether B. thuringiensis was able to reproduce in insect cadavers and form new transmission stages and we investigated whether T. castaneum larvae can get infected cannibalizing infected cadavers, opening that way possibilities for effective dispersal by infections in nature. The main aim of Chapter III was gaining deeper insight into the microbial communities associated to different lines and different life stages of T. castaneum. In addition we screened for chemical differences in external secretion profiles between different beetle lines and examined the effect of one major component of beetle’s external secretion to microbes associated to different body parts of the beetle. Our hypothesis was that various T. castaneum lines will differ in their microbial composition and that the substances excreted to the environment will have an influence on the surrounding microbiota, but also to the microbes harbored in the gut.

microbiota, Tribolium castaneum, Bacillus thuringiensis, immune memory, immune priming, insects

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