The role of Pseudomonas aeruginosa alkaline protease in activation of the antimicrobial activity in Galleria mellonella larvae

The role of Pseudomonas aeruginosa metalloprotease - alkaline protease in activation of the antimicrobial activity in Galleria mellonella larvae was investigated. The results of our in vivo study showed that injection of alkaline protease at a sublethal dose enhanced the antimicrobial activity in the hemolymph of G. mellonella larvae as a result of induction of defense peptides synthesis. We observed that the antibacterial activity against E. coli appeared in the hemolymph 4 h after the injection of both metalloprotease or heat-killed P. aeruginosa, reached the maximum level 24 h post injection, and next decreased slightly. Antifungal activity against A. niger was detected in the hemolymph 15 h and 24 h after the challenge in the case of the alkaline protease and P. aeruginosa cell treatment, respectively. We also noted that the antimicrobial activity level induced by the presence of the metalloprotease in the hemolymph was higher than the activity measured after the injection of the insects with P. aeruginosa. The results of our in vitro studies indicated that inducible antimicrobial peptides present in the hemolymph of protease- or P. aeruginosa-challenged larvae were digested by alkaline protease.