Inhibition of Plasmodium berghei Development in Mosquitoes by Effector Proteins Secreted from Asaia sp. Bacteria Using a Novel Native Secretion Signal

Abstract

Novel interventions are needed to prevent the transmission of the Plasmodium parasites that cause malaria. One possible method is to supply mosquitoes with antiplasmodial effector proteins from bacteria by paratransgenesis. Mosquitoes have a diverse complement of midgut microbiota including the Gram-negative bacteria Asaia bogorensis. This study presents the first use of Asaia sp. bacteria for paratransgenesis against P. berghei. We identified putative secreted proteins from A. bogorensis by a genetic screen using alkaline phosphatase gene fusions. Two were secreted efficiently: a siderophore receptor protein and a YVTN beta-propeller repeat protein. The siderophore receptor gene was fused with antiplasmodial effector genes including the scorpine antimicrobial peptide and an anti-Pbs21 scFv-Shiva1 immunotoxin. Asaia SF2.1 secreting these fusion proteins were fed to mosquitoes and challenged with Plasmodium berghei-infected blood. With each of these effector constructs, significant inhibition of parasite development was observed. These results provide a novel and promising intervention against malaria transmission.

Mosquito-Borne Diseases Emergence/Resurgence and How to Effectively Control It Biologically

“…To make malaria vectors inefficient, interruption of the cycle within the vector to stop parasite development before the Anopheles host becomes infective is a good solution [163]. The simplest approach to this is paratransgenesis, consisting of producing bacterial strains that are able to both live in the midgut of various mosquito species and spread rapidly among wild mosquito populations [164].…”

Reciprocal interactions between Leishmania and their microenvironments during infection in the sand fly gut and human macrophages

“…As mentioned in Chapter I, it is important to understand the overall biology in the insect vectorparasitemicrobiome relationship, as manipulation in one of these entities can result in positive or negative outcomes in another depending on the disease model. Previous reports in other insect vectors of disease have shown the importance of the gut microbiome during parasite infection and altered vector competence [29,39,77,78,85,87,171,180,181]. Unlike the importance of the undisturbed native gut microbiome during parasite infection in sand flies as we have shown in Chapters II and III, other parasites within insect vectors can augment their overall burden when the gut microbiome is altered.…”

“…In fact, in all kinetoplastid trypanosomes, receptor-mediated uptake of chelated iron has been shown only in T. brucei [210]. Overexpression of a siderophore receptor and a beta-propeller gene in the symbiont Asaia bogorensis which was fed to Anopheles mosquitoes before challenged with a Plasmodium-infected blood meal reduced overall parasite burden, suggesting the sequestration of soluble iron in the gut of the mosquitoes before infection creates a microenvironment less suitable for parasites [180]. This leads to our next hypothesis that Leishmania replication and differentiation to metacyclic parasites is driven metabolically, where parasites "sense" a lack of nutrients and increased competition to sequester soluble molecules in the gut environment, which promotes metacyclogenesis to the terminally differentiated metacyclic life form [15,17,34,165].…”

“…There are several viable methods for insect vector control including paratransgenesis of native insect gut symbionts to express anti-parasitic factors, Wolbachia infections, or genetic modification. Paratransgenesis has been successfully demonstrated in Anopheles mosquitoes against malaria parasites [180,[240][241][242].…”

“…Paratransgenesis can also be effective as an indirect mechanism against parasite infection. As alluded to in Chapter III, when mosquitoes are fed A. bogorensis that express a siderophore able to sequester soluble iron reducing the availability of this nutrient in the gut results in decreased parasite burden when fed infected blood [180]. Tsetse flies and reduviid bugs have also implemented paratransgenesis as a successful method to combat against both African and American trypanosomiasis.…”