Isolation of the symbiotic bacterium Brevundimonas aurantiaca and its regulatory effect on the autogeny of Culex pipiens pallens

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. Continuous multi-generational treatment 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 and exhibits a smooth, intact surface and a characteristic rod morphology arranged in short chains. B. aurantiaca successfully colonized in the midgut of anautogenous Cx. pipiens pallens and achieved vertical transmission. qRT-PCR analysis revealed that B. aurantiaca significantly upregulated the expression of several key reproductive genes in anautogenous Cx. pipiens pallens , including vitellogenin ( Vg1 , Vg3 ), vitellogenin receptor ( VgR ), ecdysone receptor ( EcR ), and insulin-like peptide receptor ( ILPR ). After several generations of symbiotic bacteria treatment, the reproductive phenotype of anautogenous Cx. pipiens pallens was significantly altered. By the fifth generation, the blood-feeding rate of adult mosquitoes was reduced to 87.72%, while the oviposition rate increased to 58.71%, and the larval development period was significantly prolonged. Conclusions The symbiotic bacterium B. aurantiaca reshapes the reproductive strategy of anautogenous Cx. pipiens pallens by modulating the reproductive endocrine and nutritional signaling pathways of mosquitoes. 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.