Exploration of bacteria associated with Anopheles mosquitoes around the world : For the prevention of transmission of malaria

Abstract: Every year, hundreds of thousands of people die from malaria. Malaria is a disease caused by parasites, which are spread by female vector mosquitoes of the genus Anopheles. Current control measures against malaria are based on drugs against the parasites and vector control using insecticides. A problem with these measures is the development of resistance, both in the parasites against the drugs and the mosquitoes against the insecticides. Therefore, additional areas of malaria control must be explored. One such area involves the bacteria associated with the vector mosquitoes. Bacteria have been shown to affect mosquitoes at all life stages, e.g. by affecting choice of oviposition site by female mosquitoes, development of larvae and susceptibility to parasite infection in adults. Furthermore, genetic modification of symbiotic bacteria has been suggested as a mean of killing the parasites in the mosquitoes. This thesis is based on four field studies and one laboratory study and aims to investigate the naturally occurring bacteria associated with different life stages of malaria mosquitoes and how they are acquired. All studies are based on amplicon sequencing of the 16S rRNA gene. We found that overall mosquitoes contain different bacterial communities. However, bacteria associated with adults reflect their life history and can predict the origin of mosquitoes. Bacteria in larvae are similar during the developmental stages but vary with breeding site. Also in larvae, the bacteria could be used to predict the origin of breeding site. Some bacteria could be related to the presence or absence of Anopheles around human habitations and the diversity of aquatic bacteria in breeding sites is large, though some taxa are common. Overall, both environmental and host-genetic factors affect the gut bacterial composition in adult females. In conclusion, this thesis contributes to increasing the knowledge of bacterial diversity associated with Anopheles mosquitoes and to provide insight into how the bacteria are acquired, which can be useful in malaria control.