Cationic protein 8 plays multiple roles in Galleria mellonella immunity

Abstract

AbstractGalleria mellonellacationic protein 8 (GmCP8) is a hemolymph protein previously identified as an opsonin and an inhibitor of fungal proteases. In this work, we showed its bactericidal activity towardPseudomonas entomophila,Pseudomonas aeruginosa,Bacillus thuringiensis,Staphylococcus aureus, andEscherichia coliand against yeast-like fungiCandida albicans. The activity againstE. coliwas correlated with bacterial membrane permeabilization. In turn, in the case ofP. entomophila,B. thuringiensis,andC. albicans, the atomic force microscopy analysis of the microbial surface showed changes in the topography of cells and changes in their nanomechanical properties. GmCP8 also showed the inhibitory activity toward the serine protease trypsin and the metalloproteinase thermolysin. The expression of the gene encoding the GmCP8 protein did not increase either in the gut or in the fat body ofG. mellonellaafter oral infection withP. entomophila. Similarly, the amount of GmCP8 in the hemolymph ofG. mellonelladid not change in immune-challenged insects. However, when GmCP8 was injected into theG. mellonellahemocel, a change in the survival curve was observed in the infected larvae. Our results shed new light on the function of GmCP8 protein in insect immunity, indicating its role in humoral defence mechanisms.