Effects of avian Plasmodium exposure on the microbiota of Culex pipiens

Malaria parasites (Plasmodium spp.) are mosquito-borne parasites that infect humans and wildlife. Several studies support the role of mosquito microbiota as a major driver of Plasmodium transmission, although studies on wildlife malaria are typically neglected. Here, we used a 16S rRNA metabarcoding approach to assess whether the exposure to avian Plasmodium parasites affects the microbiota of their natural vector, Culex pipiens. Mosquitoes, captured in the field as larvae and grown in the laboratory, were allowed to feed on house sparrows (Passer domesticus) naturally infected with Plasmodium relictum (lineage SGS1) and uninfected birds. We analyzed the microbiota composition of the abdomens of individual mosquitoes and found 2,006 Amplicon Sequence Variants (ASVs). Culex pipiens' microbiota was dominated by bacteria of the genus Wolbachia, followed by the genera Stenotrophomonas and Faecalibacterium. We observed no difference in alpha nor beta diversity between mosquitoes that fed on Plasmodium-infected birds (exposed mosquitoes) and those that fed on uninfected birds (unexposed mosquitoes). However, exposed mosquitoes had a higher relative abundance of bacteria of the family Bacteroidaceae and the genus Bacteroides than the unexposed mosquitoes. Excluding the intracellular endosymbiont Wolbachia from the analyses, we obtained similar results, and also found a higher relative abundance of bacteria of the family Rikenellaceae in exposed mosquitoes. A pathway enrichment analysis based on KEGG annotations revealed that the bacterial community in exposed mosquitoes was enriched in pathways mainly related to biosynthesis and metabolism. Our results suggest that Cx. pipiens exposed to avian Plasmodium have slightly different microbiota composition, although further research is needed to establish the causality of these effects.