Fig. 1

Interactions between the microbiota and Plasmodium in the mosquito midgut. The microbiota affects Plasmodium infection by several mechanisms: (i) Direct impact on parasites via inhibition of its oxidative defence system [13, 20] or by production of uncharacterised antimicrobials [16, 22]. (ii) Stimulation of the NF-κB dependent Immune-deficiency (Imd) pathway, which is regulated by Peptidoglycan Recognition Proteins (PGRPs) and restrains parasite infection [15, 30]. The mechanisms of action of the Imd pathway on parasites are still unclear, they probably include TEP1-dependent and independent components [5, 18, 19]. (iii) Blood meal inducible physical barriers affect gut microbes: a dityrosine network reduces the diffusion of elicitors, thus protecting the microbiota and Plasmodium from immune activation [32] and the microbiota-dependent induction of the peritrophic matrix [24] may have positive and/or negative impacts on parasite infection. Reciprocally, Plasmodium infection inhibits antioxidant enzymes in the mosquito gut, which has been suggested to help parasite infection via a reduction of the mosquito microbiota [21]