Detection and partial characterization of extracellular proteases of the pathogenic fungi Endocronartium pini, Gremmeniella abietina and Heterobasidion annosum

Protease activities from 10 homokaryotic isolates of Heterobasidion annosum, two isolates of Gremmeniella abietina and six isolates of Endocronartium pini were studied. All the fungi showed in vitro protease activity with denatured casein. The greatest caseinolytic activity was at acidic pH, but Heterobasidion annosum and Gremmeniella abietina showed caseinolytic activity at basic pH also. Protease preparations from Heterobasidion annosum were able to degrade proteins from total phloem extracts of Pinus sylvestris, Picea abies, Betula pendula and Juniperus communis. At basic pH the artificial substrates hippuryl arginine (HA) and hippuryl phenylactic acid (HPLA), were hydrolysed most rapidly by Heterobasidion annosum at pH 8.1, indicating high exopeptidase activity at this pH. According to inhibitor studies with EDTA (ethylenediaminetetraacetic acid), E64 (L-trans-epoxysuccinyl-leycylamide-(4-guanidino)-butane-agmatine) and pin2 (potato trypsin/chymotrypsin inhibitor) both cysteine and serine proteases were present in proteases secreted by these pathogens, although only very low protease activity at basic pH was detected with Endocronartium pini.