Functional genomic analyses of Enterobacter, Anopheles and Plasmodium reciprocal interactions that impact vector competence

Abstract

BackgroundMalaria exerts a tremendous socioeconomic impact worldwide despite current control efforts, and novel disease transmission-blocking strategies are urgently needed. The Enterobacter bacterium Esp_Z, which is naturally harboured in the mosquito midgut, can inhibit the development of Plasmodium parasites prior to their invasion of the midgut epithelium through a mechanism that involves oxidative stress. Here, a multifaceted approach is used to study the tripartite interactions between the mosquito, Esp_Z and Plasmodium, towards addressing the feasibility of using sugar-baited exposure of mosquitoes to the Esp_Z bacterium for interruption of malaria transmission.MethodsThe ability of Esp_Z to colonize Anopheles gambiae midguts harbouring microbiota derived from wild mosquitoes was determined by qPCR. Upon introduction of Esp_Z via nectar feeding, the permissiveness of colonized mosquitoes to Plasmodium falciparum infection was determined, as well as the impact of Esp_Z on mosquito fitness parameters, such as longevity, number of eggs laid and number of larvae hatched. The genome of Esp_Z was sequenced, and transcriptome analyses were performed to identify bacterial genes that are important for colonization of the mosquito midgut, as well as for ROS-production. A gene expression analysis of members of the oxidative defence pathway of Plasmodium berghei was also conducted to assess the parasite’s oxidative defence response to Esp_Z exposure.ResultsEsp_Z persisted for up to 4 days in the An. gambiae midgut after introduction via nectar feeding, and was able to significantly inhibit Plasmodium sporogonic development. Introduction of this bacterium did not adversely affect mosquito fitness. Candidate genes involved in the selection of a better fit Esp_Z to the mosquito midgut environment and in its ability to condition oxidative status of its surroundings were identified, and parasite expression data indicated that Esp_Z is able to induce a partial and temporary shutdown of the ookinetes antioxidant response.ConclusionsEsp_Z is capable of inhibiting sporogonic development of Plasmodium in the presence of the mosquito’s native microbiota without affecting mosquito fitness. Several candidate bacterial genes are likely mediating midgut colonization and ROS production, and inhibition of Plasmodium development appears to involve a shutdown of the parasite’s oxidative defence system. A better understanding of the complex reciprocal tripartite interactions can facilitate the development and optimization of an Esp_Z-based malaria control strategy.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-016-1468-2) contains supplementary material, which is available to authorized users.

Microbiome Interaction Networks and Community Structure From Laboratory-Reared and Field-Collected Aedes aegypti, Aedes albopictus, and Culex quinquefasciatus Mosquito Vectors

“…Host pathways and processes known to influence microbiota in mosquitoes include immunity, amino acid metabolism, reactive oxygen species, and calcium transport ( Kumar et al, 2010 ; Stathopoulos et al, 2014 ; Pang et al, 2016 ; Short et al, 2017 ; Xiao et al, 2017 ; Zhao et al, 2017 ). Additionally, serial passaging of gut symbionts in mosquitoes selected for isolates that persist in the gut for longer periods of time ( Riehle et al, 2007 ; Dennison et al, 2016 ), indicating that bacterial genetics is also important in shaping the microbiome.…”

Gut microbiota is essential in PGRP-LA regulated immune protection against Plasmodium berghei infection

“…Another stably inherited gut commensal bacteria, Asaia, can be genetically modified and directly inhibits pathogen development by secreting antiplasmodial effectors [23]. In addition, these microbes inhibit parasites indirectly through promoting the formation of PM and stimulating the oxidative defense system and NF-κB dependent immune responses [24][25][26][27].…”

Novel Wolbachia strains in Anopheles malaria vectors from Sub-Saharan Africa

“…Numerous studies have shown that certain species of bacteria can inhibit Plasmodium development [2][3][4]. For example, Enterobacter bacteria that reside in the Anopheles midgut can inhibit the development of Plasmodium parasites prior to their invasion of the midgut epithelium [5,6].Wolbachia endosymbiotic bacteria are estimated to naturally infect ~40% of insect species [7] including mosquito vector species that are responsible for transmission of human diseases such as Culex (Cx.) quinquefasciatus [8][9][10] and Aedes (Ae.)…”

“…Numerous studies have shown that certain species of bacteria can inhibit Plasmodium development [2][3][4]. For example, Enterobacter bacteria that reside in the Anopheles midgut can inhibit the development of Plasmodium parasites prior to their invasion of the midgut epithelium [5,6].…”