Isolation of the symbiotic bacterium Brevundimonas aurantiaca and its potential role in modulating reproductive traits in Culex pipiens pallens

Abstract Background Culex pipiens pallens is a significant vector of mosquito-borne diseases, and its autogenous trait exerts a critical impact on population expansion and disease transmission risks. Understanding the regulatory effect of gut-specific symbiotic bacteria on the autogeny of Cx. pipiens pallens will provide a microbial perspective to elucidate the mechanisms underlying the formation of autogenous reproductive strategies and provide a theoretical basis for the development of novel mosquito-borne disease control. Methods Autogenous Cx. pipiens pallens were utilized to isolate and culture gut-specific symbiotic bacteria. Green fluorescent protein (GFP) labeling technology and absolute quantitative real-time polymerase chain reaction (qRT-PCR) were used to confirm the colonization ability of the symbiotic bacteria in the guts of anautogenous Cx. pipiens pallens . The alterations in the expression levels of reproductive-related genes were verified by relative qRT-PCR. 20-Hydroxyecdysone (20E), juvenile hormone (JH), and the concentrations of vitellogenin were measured to assess the vitellogenesis. Continuous multi-generational treatment with bacteria was applied to anautogenous Cx. pipiens pallens to evaluate transgenerational effects. Larval stage, pupation rate, pupal stage, emergence rate, male:female ratio, blood-feeding rate, oviposition rate, and hatching rate were recorded to assess the effects of the symbiotic bacteria on the reproductive and developmental phenotypes in the anautogenous Cx. pipiens pallens . Results The gut-specific symbiotic bacterium isolated from autogenous Cx. pipiens pallens was identified as Brevundimonas aurantiaca , a Gram-negative rod-shaped bacterium that forms orange-yellow circular colonies on Caulobacter medium. B. aurantiaca successfully colonized in the midgut of anautogenous Cx. pipiens pallens and achieved vertical transmission. The reproductive phenotype of anautogenous Cx. pipiens pallens is complex and significant alterations were observed in two aspects investigated. By the fifth generation, the bacteria-treated group compared with the untreated anautogenous group showed decreased blood-feeding rate (87.7% vs 96.3%) and prolonged larval development (8.3 d vs 7.4 d). Conclusions The symbiotic bacterium B. aurantiaca may be associated with changes in the reproductive strategy of anautogenous Cx. pipiens pallens , although direct mechanistic evidence is not provided in this study. These findings not only provide an important microbial regulatory perspective for understanding the molecular mechanisms underlying autogeny in mosquitoes, but also offer potential targets for the development of novel symbiont-based biocontrol strategies against mosquito-borne diseases.