Transgenic expression of antimicrobial peptides from black soldier fly enhance resistance against entomopathogenic bacteria in the silkworm, Bombyx mori

Antimicrobial peptides (AMPs) are effective molecules produced by the innate immune system of most organisms to fend off invading microbes and regarded as promising alternatives to conventional antibiotics due to their potent antimicrobial activities. The larvae of black soldier fly (BSF), Hermetia illucens, inhabit microbe-rich environments and its insect genome encodes a broad repertoire of AMPs. In the present study, three AMPs encoded by BSF Hidefensin-1, Hidiptericin-1 and HiCG13551 were cloned, expressed and purified in a recombinant Escherichia coli expression system. In vitro, both Hidefensin-1 and Hidiptericin-1 inhibited the growth of Streptococcus pneumoniae and Escherichia coli, while HiCG13551 inhibited the growth of Staphylococcus aureus and E. coli. Transmission electron microscopy showed that Hidiptericin-1 inhibited bacterial growth through bacterial membrane lysis. We also constructed a transgenic silkworm line constitutively expressing an AMP cassette HiAMP4516 encoding all the three AMPs, and the silkworms showed an increased resistance to both gram positive and gram-negative entomopathogenic bacteria. These results provide insights into the antibacterial activities of BSF AMPs both in vitro and in vivo and suggest a great potential of exploiting insect-derived AMPs in silkworm disease resistance breeding.