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Title: Reactive oxygen species and antioxidant enzymes in the Lutzomyia-Leishmania system
Author: Díaz Albíter, Héctor Manuel
ISNI:       0000 0004 2732 390X
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2011
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Female phlebotomines are the vectors of Leishmania protozoa. Leishmania reside in the gut of the sand fly and they share this niche with different microbes that interact with either sand fly or Leishmania. Reactive Oxygen Species (ROS) are a major component of the insect innate immune system regulating gut-microbe homeostasis in other insects but the importance of this component in sand flies and its impact on Leishmania is unknown. The sand fly ROS system was initially investigated by examining the expression of antioxidant genes in the midgut of Lu. longipalpis throughout blood digestion using semi-quantitative RT-PCR. Antioxidant genes were differentially expressed throughout digestion and exhibited a peak at 48 h after blood feeding. Catalase was the most upregulated gene. Sand fly fecundity was affected by age and redox balance, as suggested by a significant reduction in egg numbers from older flies as well as after RNAi- mediated silencing of catalase. ROS detoxification appeared to be important during egg development as suggested by the accumulation of catalase in developing oocytes as well as an increase in egg numbers after antioxidant per os supplementation. Sand fly longevity was affected by redox balance, as shown by a significant reduction in survival after RNAi-mediated abrogation of catalase. Dietary addition of antioxidant failed to rescue early mortality, but this group also showed higher levels of phenoloxidase, a potential indicator of bacterial infection. Antioxidant genes were differentially expressed in Leishmania and Serratia colonised guts. Overall, midguts exhibited downregulation of ROS-detoxifying enzymes while Serratia-infected ones displayed the opposite trend. RNAi-silencing of catalase reduced Leishmania populations in the midgut suggesting that oxidative stress is deleterious to this protozoan. Dietary addition of the antioxidant uric acid in Serratia-infected flies increased sand fly mortality as in previous experiments with vitamin C. Although Serratia CFUs were significantly lower in the group with the highest mortality, the population of the resident microbiota was significantly higher in the same group. Interestingly, the numbers of resident microbiota were even higher in flies not infected with Serratia. The implications of the results are discussed in relation to gut immune homeostasis in other insect-microbe systems as well as the possibility of applying some of this information towards understanding the systems governing adult longevity in relation to vectorial capacity and the improvement of sand fly control.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral