Regulation of extracellular proteinase production in an ectomycorrhizal fungus Hebeloma crustuliniforme

Abstract

Hebeloma crustuliniforme was grown in defined liquid media containing different combinations of ammonium, glucose, and bovine serum albumin as sources of nitrogen and carbon for proteinase induction or repression. The production of extracellular proteinase was highest in the medium containing bovine serum albumin as sole nitrogen source and it was not affected by the addition of ammonium at concentrations below 3.2 mM, but higher ammonium concentrations repressed the proteinase production. Proteinase synthesis required simple carbon as an energy source and was not repressed by glucose at concentrations from 0.5 to 2%. Optimal culture pH for proteinase production was between 4 and 5. At pH 3, the fungus yielded biomass only 10% of that at pH 5, though proteinase production per mg dry weight of mycelium was not affected. The fungus was unable to grow and produce proteinase at pH 7 or above. The proteinase was most active at pH 2.5–3 and stable at pH 2.5-5.5. These results suggest that the regulation of extracellular acid proteinase in H. crustuliniforme involves protein induction and partial nitrogen repression but not carbon catabolite repression.

Key Words:

• Hebeloma crustuliniforme
• mycorrhizal fungus
• proteinase