Carbon nutrition and hydrolytic and cellulolytic activities in the ectomycorrhizal fungus Pisolithus tinctorius

Abstract

Four strains of an ectomycorrhizal fungus, Pisolithus tinctorius, were investigated for carbon nutrition, and for production of hydrolytic and cellulolytic enzymes. Glucose, mannose, and cellobiose supported rapid mycelial growth of all four strains. Fructose was utilized by two strains, SMF and S359. Of the 10 hydrolytic enzymes examined, acid phosphatase, acid α-galactosidase, acid esterase, and acid β-glucosidase were found in all four strains. β-Galactosidase was only observed in strain S359. α-Mannosidase, β-mannosidase, α-glucosidase, β-xylosidase, and proteinase were not detected in any of the four strains. Isozyme patterns of β-glucosidase and esterase in the four strains were compared by activity staining after native gradient gel electrophoresis. The isozyme pattern of β-glucosidase showed three major forms in all four strains. In addition, two more isoforms were found in strain S370. All strains shared two esterase bands, while strain S370 had three more isoforms. Study on strain SMF indicated that acid β-glucosidase was expressed constitutively, with increased activity in cellobiose-containing media. Under nitrogen-limiting conditions, a low level of endoglucanase and exoglucanase activity was observed in strains SMF and S359. Further study on S359 showed that high concentrations of nitrogen repressed the cellulolytic activity. When cellobiose served as carbon source, higher cellulolytic activity was observed. Cellulose did not induce higher activity.Key words: Pisolithus, ectomycorrhizal, β-glucosidase, hydrolytic enzymes, cellulolytic enzymes.