Silk components and properties of the multilayer cocoon of the greater wax moth, Galleria mellonella.

The greater wax moth Galleria mellonella is a major pest of brood combs, and produces large quantities of strong, elastic silk in the environment. However, little research has been conducted on the silk glands (SGs), silk composition and functions of G. mellonella. In this study, we compared the morphologies of the SGs of G. mellonella and Bombyx mori and found that the nuclei of the anterior SGs differ distinctly. We also investigated the protein components and morphology of the G. mellonella cocoon in terms of its multilayer structure. Proteomic analyses identified 158 secretory proteins across the various cocoon layers. Fibroin, sericin, seroin and adhesive proteins were the most abundant proteins. The expression patterns of the major silk genes were investigated, and the results revealed the specific expression of P16 and Seroin3 genes in the anterior SG. Scanning electron microscopy and proteomic analyses of the cocoon layers showed that the sericin contents in the outermost and middle layers were significantly higher than that in the innermost layer. We extracted the soluble proteins from the different cocoon layers and evaluated their antimicrobial activities in vitro. Only the outermost cocoon layer showed antibacterial activity against Escherichia coli. Mechanical property tests showed that G. mellonella silk was stronger than B. mori silk. Our study provides important information on the composition and properties of G. mellonella cocoon silk, and serves as a basis for future research and use.