Proteases and Their Involvement in the Infection and Immobilization of Nematodes by the Nematophagous Fungus Arthrobotrys oligospora

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The nematophagous fungus Arthrobotrys oligospora produced extracellular proteases when grown in a liquid culture, as revealed by measuring the hydrolysis of the chromogenic substrate Azocoll. The extracellular protease activity was inhibited by phenylmethylsulfonyl fluoride (PMSF) and other serine protease inhibitors and partly inhibited by the aspartate protease inhibitor pepstatin and by a cysteine protease inhibitor [l-trans-epoxysuccinyl-leucylamide-(4-guanidino)-butane, or E-64]. Substrate gel electrophoresis showed that the fungus produced several different proteases, including multiple serine proteases. The function of proteases in the infection of nematodes was examined by treating the fungus with various protease inhibitors. None of the inhibitors tested affected the adhesion of nematodes to the traps, but incubating trap-bearing mycelium with a serine protease inhibitor, PMSF, antipain, or chymostatin, or the metalloprotease inhibitor phenanthroline significantly decreased the immobilization of nematodes captured by the fungus. Inhibitors of cysteine or aspartic proteases did not affect the immobilization of captured nematodes. The effects of PMSF on the immobilization of nematodes were probably due to serine proteases produced by the fungus, since the effects were observed when unbound inhibitor was washed away from the fungus before the nematodes were added to the system. No effects were observed when the nematodes only were pretreated with PMSF.

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