Secretion of Malaria Transmission-Blocking Proteins from Paratransgenic Bacteria

Malaria is a debilitating and deadly disease that afflicts over 200 million people and kills over 600 thousand each year. Due to quickly evolving drug resistance and lack of an affordable vaccine, novel interventions are needed to fight the Plasmodium parasites that cause malaria. Targeting Plasmodium inside their mosquito hosts is one approach that could complement other preventative and medicinal interventions by reducing the ability of the mosquitoes to transmit the disease to humans. The research presented here uses paratransgenesis, the genetic modification of symbiotic bacteria within the mosquito midgut, to provide antimalarial protein to the mosquito and to interfere with the life cycle of Plasmodium within the insect host. This research has produced three new antimalarial paratransgenic tools. The first tool is a set of new antimalarial effector proteins that were constructed by converting anti-Plasmodium mouse antibodies into single-chain variable fragment (scFv) versions for expression by bacteria. These antibodies bind to Plasmodium surface proteins and interfere with critical steps in the parasite life cycle. The second tool is a modified bacterial species, Pantoea agglomerans , which was engineered to secrete diverse antimalarial proteins via the hemolysin secretion pathway. Modified P. agglomerans were fed to mosquitoes and were capable of inhibiting the invasion of Plasmodium within the midgut. The third tool is another modified bacterial species, Asaia sp. SF2.1. Native Type II secretion signals were discovered that enable the creation of paratransgenic strains of these bacteria. Modified strains of Asaia sp. SF2.1 were also demonstrated to interfere with the invasion of Plasmodium within the mosquito. These tools have laid the groundwork for the future use of paratransgenic bacteria to combat malaria in the wild. Asaia sp. SF2.1 bacteria, in particular, are capable of spreading throughout mosquito populations, so they provide their own drive mechanism to establish themselves within the mosquito vectors of malaria. While further modifications will be required to make these bacteria ready for field use, the findings of this research provide proof of concept that the bacteria are suitable for eventual use in malaria transmission-blocking interventions