Metagenome sequencing reveals the midgut microbiota makeup of Culex pipiens quinquefasciatus and its possible relationship with insecticide resistance

Midegut microbiota can participate in the detoxification and metabolism processes of insects, but there are few reports on the relationship between midgut microbiota and insecticide resistance in mosquitoes. In this study, we selected a susceptible strain (SS), a field-collected Hainan strain (HN), and a deltamethrin-resistant strain (RR) of Culex pipiens quinquefasciatusand performed metagenomic sequencing on them to understand the diversity and functions of their midgut microbiota. The results showed that there were differences in midgut microbiota between the three strains of Cx. pipiens quinquefasciatus. At the phylum level, Proteobacteria was the most prominent, accounting for nearly 70% of their midgut microbes. At the genus level, Aeromonas made up the highest proportion. In addition, Aeromonas, Morganella, Elizabethkingia, Enterobacter, CedeceaSerratia, and Thorsellia showed significant differences between strains. At the species level, Bacillus cereus, Enterobacter cloacae complex sp. 4DZ3-17B2, Streptomyces sp. CNQ329, and Pseudomonas and Wolbachia were more abundant in the two resistant strains. Principal component analysis (PCA) showed that the SS strain had significantly different metagenomic functions than the two deltamethrin-resistant strains (HN and RR strain). Compared with the SS strain, HN and RR strain showed differences in more than 10 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Further investigation of the KEGG Orthology pathways revealed that differentially expressed pathway K15001 was annotated as the CYP4 superfamily. Through random forest prediction, it was found that Macrococcus caseolyticus was very important for the classification of the three groups of samples, and differentially expressed genes encoding detoxification enzymes were annotated in it. The annotation results of the differentially expressed genes of Candidatus Pacearchaeota archaeon revealed a sodium-dependent transporter, which may be related to the insensitivity of its Na+ ion channels. Pseudomonas syringae may be involved in the metabolic processing of insecticides. Our analysis of species abundance and functional diversity can provide directions for future studies.