HEMICELLULOLYTIC ENZYMES IN P-STRAINS AND S-STRAINS OF HETEROBASIDION-ANNOSUM

The secretion of several hemicellulolytic enzymes and endoglucanase was studied in S- and P-group strains of a wood-rotting pathogen, Heterobasidion annosum, using enzyme activity assays and isoelectric focusing. In liquid cultures supplemented with birch sawdust or pure xylan, both strains of the fungus produced xylanases, mannanases, endoglucanases and alpha-galactosidases. Low activities were detected in cultures containing only glucose as a carbon source. When S-strain cultures were provided with a carrier matrix, protein secretion to the culture medium started earlier and was significantly increased compared to free cell cultures. This was not the case with the P-strain. In both strains of H. annosum the pH of the birch sawdust culture medium fell within 12 d to below 3.5, and then started to increase towards the end of the cultivation period. The increase in ph appeared to correlate with the formation of hemicellulolytic and endoglucanase activities. The isoenzyme patterns of xylanase, mannanase and endoglucanase were typical for P- and S-strains. In P-strain cultures containing xylan, a xylanase with an alkaline pi value was induced which, however, was absent when the P-strain was grown with the birch sawdust substrate. In the P-strain the mannanase pattern at the early stage of growth was comparable to that of the S-strain at the later stages of growth on birch sawdust medium. Later in the growth of the P-strain, this pattern was replaced by mannanases with more acid pI values. The relative intensities of the individual endoglucanases varied between the P- and S-strains.