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

Midegut microbiota canparticipate in the detoxification and metabolism processes of insects, butthere are few reports on the relationship between midgut microbiota and insecticideresistance in mosquitoes. In this study, we selected a susceptible strain (SS), afield-collected Hainan strain (HN), and a deltamethrin-resistant strain (RR) ofCulexpipiens quinquefasciatusand performed metagenomic sequencing on themto understand the diversity and functions of their midgut microbiota. Theresults showed that there were differences in midgut microbiota between thethree strains of Cx. pipiens quinquefasciatus. At the phylum level,Proteobacteria was the most prominent, accounting for nearly 70% of their midgutmicrobes. At the genus level, Aeromonas made up the highest proportion. In addition, Aeromonas, Morganella, Elizabethkingia,Enterobacter, Cedeceaand Thorselliashowed significant differences between strains. At the species level,Bacillus cereus, Enterobacter cloacae complexsp. 4DZ3-17B2, Streptomyces sp. CNQ329, and Pseudomonas and Wolbachiawere more abundant in the two resistant strains. Principal component analysis (PCA) showed that the SS strain had significantly differentmetagenomic functions than the two deltamethrin-resistant strains (HN and RRstrain). Compared with the SS strain, HN and RR strain showed differences in morethan 10 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Furtherinvestigation of the KEGG Orthology pathways revealed that differentiallyexpressed pathway K15001 was annotated as the CYP4 superfamily. Through randomforest prediction, it was found that Macrococcuscaseolyticus was very important for the classification of the three groupsof samples, and differentially expressed genes encodingdetoxification enzymes were annotated in it. The annotation results of thedifferentially expressed genes of Candidatus Pacearchaeota archaeon revealed a sodium-dependenttransporter, which may be related to the insensitivity of its Na+ion channels. Pseudomonas syringaemay be involved in the metabolic processing of insecticides. Our analysis ofspecies abundance and functional diversity can providedirections for future studies.