Role of Proteases in Penetration of Insect Gut by the Entomopathogenic Nematode Steinernema glaseri (Nematoda: Steinernematidae)

Abstract

The entomopathogenic nematode Steinernema glaseri enters into the host through natural openings and penetrates through the internal walls before entering into the hemocoel. In the present study we found that in addition to mechanical means used for penetration, entomopathogenic nematodes release proteolytic enzymes. When nematodes were treated with protease inhibitors and injected into Galleria mellonella gut, the percentage mortality of G. mellonella was reduced to 17 ± 2 for iodoacetamide and 30 ± 4 for 1,10-phenanthroline-treated nematodes compared to 75 ± 3 for control after 18 hr post anal injection. Treatment of the nematodes with combinations of protease inhibitors and protein synthesis inhibitors did not result in a synergistic effect on G. mellonella mortality. Nematode penetration of G. mellonella gut after their treatment with iodoacetamide and 1,10-phenanthroline was reduced to 13.4 ± 1.1 and 15.6 ± 1.9, respectively, after 12 hr postinjection through the anus. The antibiotic chloramphenicol inhibited the symbiotic bacteria Xenorhabdus poinarii cells and reduced the average viable number retained/100 nematodes to 40 ± 30. Cycloheximide delayed G. mellonella mortality but not gut penetration. This suggests that it might have some toxic effect on the nematodes.