ABSTRACT
Purified acidic protease [PII] from the infective juveniles [IJs] of entomopathogenic nematode Heterorhabditis bacteriophora EB7, as an effective biocontrol agent against a wide variety of insect pests, has been characterized. The effect of temperature stress on infectivity of the IJs was also examined. Exposure of IJs of H. bacteriophora EB7 to high temperatures above 35[degree]C accounts for a rapid decline in nematode survival and infectivity. Temperatures above 35[degree]C have deleterious effect on the activity and stability of H bacteriophora protease PII. Enzyme activity was maximal at pH 5.0 and 35[degree]C. H. bacteriophora protease PII degraded a variety of protein substrates including azocasein, azocoll, casein, hemoglobin, collagen and gelatin with different ratios. Enzyme activity was totally abolished by 1 microM pepstatin A, not affected by activators or inhibitors of cysteine, serine and metalloprotease. Substrate specificity, pH optimum and inhibitors sensitivity studies revealed that it is an aspartic protease and comparable with cathespsin D-like enzyme. H. bacteriophora aspartic protease seems to be implicated in tissue penetration and plays a specific role during molting of the IJs within an insect host. It is recommended to spray IJs as potential biocontrol agent on the field at the sunset or in the early morning to avoid the temperature stresses on IJs. These results were compared with other previously reported proteases from animal parasitic nematodes