ROLE OF PROTEASES IN PENETRATION OF INSECT GUT BY THE ENTOMOPATHOGENIC NEMATODE STEINERNEMA-GLASERI (NEMATODA, STEINERNEMATIDAE)

The entomopathogenic nematode Steinernema glaseri enters into the host through natural openings and penetrates through the internal walls be fore entering into the hemocoel. In the present study we found that in addition to mechanical means used for penetration, entomopathogenic n ematodes release proteolytic enzymes. When nematodes were treated with protease inhibitors and injected into Galleria mellonella gut, the pe rcentage mortality of G. mellonella was reduced to 17 +/- 2 for iodoac etamide and 30 +/- 4 for 1,10-phenanthroline-treated nematodes compare d to 75 +/- 3 for control after 18 hr post anal injection. Treatment o f the nematodes with combinations of protease inhibitors and protein s ynthesis inhibitors did not result in a synergistic effect on G. mello nella mortality. Nematode penetration of G. mellonella gut after their treatment with iodoacetamide and 1,10-phenanthroline was reduced to 1 3.4 +/- 1.1 and 15.6 +/- 1.9, respectively, after 12 hr postinjection through the anus. The antibiotic chloramphenicol inhibited the symbiot ic bacteria Xenorhabdus poinarii cells and reduced the average viable number retained/100 nematodes to 40 +/- 30. Cycloheximide delayed G. m ellonella mortality but not gut penetration. This suggests that it mig ht have some toxic effect on the nematodes. (C) 1995 Academic Press, I nc.