Characterization of Antibacterial Peptides in Culex pipiens (Diptera: Culicidae) in Response to Bacillus sphaericus infection

Antimicrobial peptides (AMPs) play a crucial role in defending mosquitoes against micro-organisms. The objective of this study was to identify AMPs produced in the hemolymph of Culex (Cx.) pipiens mosquitoes following bacterial infection. Mosquito larvae were collected from the Nahia drainage conduit in Giza Governorate and treated with Bacillus sphaericus strain 2362. The lethal concentration (LC50 and LC80) values were determined at concentrations of 0.042 and 0.174 ppm, respectively. The protein profiles of both treated and untreated Cx. pipiens mosquito larvae were analyzed using SDS-PAGE in a Bio-Rad cell. The analysis revealed the presence of several polypeptides, including Megacin β, α, and γ forms (15, 29.2, and 39.8 kDa), Gambicin (7.5 kDa), Diptericin (9.4 kDa), Attacin (23.8 kDa), and Subtilisin (27.6 kDa). Additionally, B. sphaericus double toxin Bin A (41.9 kDa) and Bin B (51.6 kDa) were observed, which are synthesized during sporulation and co-crystallize within bacteria. Furthermore, soluble mosquitocidal toxins Mtx1 (98.6 kDa) and Mtx2 (31 kDa) produced during vegetative growth were identified. Lastly, the two-component crystalline toxins Cry48Aa1 (135 kDa) and Cry49Aa1 (52.8 kDa) were detected. Understanding the mechanism behind mosquito resistance to bacterial pathogens is essential for developing strategies to combat this resistance.