Banca de DEFESA: JÉSSICA FIOROTTI DE PAULO

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : JÉSSICA FIOROTTI DE PAULO
DATE: 13/05/2022
TIME: 09:00
LOCAL: Internet - Zoom
TITLE:

Effect of Metarhizium spp. in the tick immune response and the effect of oxidative stress on the control of these parasites

KEY WORDS:

Biological control; hemocytes; entomopathogenic fungi; phagocytosis; autophagy.

PAGES: 179
BIG AREA: Ciências Agrárias
AREA: Medicina Veterinária
SUBÁREA: Medicina Veterinária Preventiva
SPECIALTY: Doenças Parasitárias de Animais
SUMMARY:

Entomopathogenic fungi (EPF) have been widely explored for their potential in the biological control of insect pests and as an ecological alternative to acaricides to limit tick infestation in the field. The arthropod cuticle is the main barrier against fungal infection, however, an understanding of the internal defense mechanisms after EPF infection in tick hemocoel is still quite limited. The present thesis evaluated the hemocytes from Rhipicephalus microplus after Metarhizium infection, using light microscopy and transmission electron microscopy approaches, as well as the evaluation of cytotoxicity. The evaluation of the function of TEPs (proteins containing thioester group) in the immunity of Ixodes ricinus was also addressed, using a quantitative analysis of the gene expression of TEPs, as well as a phagocytic assay followed by gene silencing. Finally, the present study sought to develop a fungal isolate tolerant to host oxidative stress, to improve its efficacy in tick control. Hemocytes had their morphology altered after EPF infection, presenting heterogeneous cytoplasm, vacuoles of different electron densities, as well as the formation of autophagosomes and subcellular material in different stages of degradation. M. robertsii propagules were more toxic to tick hemocytes at the highest concentration tested. Regarding the gene expression profile, a positive regulation was observed in the expression of 6 genes in relation to the control group, 2h after EPF infection. After gene silencing, hemocytes from EPF-infected ticks showed significant reductions in phagocytosis rates when compared to the control group, with IrC3-3 silencing the most expressive, resulting in a 60% reduction in the phagocytic index. Furthermore, the tick survival time was longer when lower fungal concentrations were used, on the other hand, when the phagocytosis action was reduced, the mean survival time decreased considerably. From the growth in subculturing in increasead doses of menadione (pro-oxidant), EPF had an increase in stress tolerance without changing its morphology and its conidial production. Furthermore, the tolerant strain of M. robertsii showed increased antioxidant defenses and increased levels of ROS in the host compared to the others. Furthermore, the induction of tolerance provided an increase in the percentage of control for R. microplus engorged females, making the strain more efficient in controlling the tick, as well as a decrease in autophagic vacuoles in host cells. In summary, this study demonstrated some survival strategies of ticks against EPF infection and how to try to circumvent them to improve fungal efficacy for the development of alternative techniques for tick control.

BANKING MEMBERS:
Presidente - 387922 - VANIA RITA ELIAS PINHEIRO BITTENCOURT
Interna - 3103528 - CLAUDIA BEZERRA DA SILVA
Interno - 3701492 - HUARRISSON AZEVEDO SANTOS
Interna - 2860277 - ISABELE DA COSTA ANGELO
Externo à Instituição - EVERTON KORT KAMP - UFG
Externo à Instituição - RUBEM FIGUEIREDO SADOK MENNA BARRETO - FIOCRUZ
Externa à Instituição - ISABEL KINNEY FERREIRA DE MIRANDA SANTOS