The production of an extracellular thermostable P-mannosidase by the thermophilic fungus Thermoascus aurantiacus Miehe was investigated in shake flask cultures. Among five different carbon sources and inducers tested, locust bean gum at 15 g l(-1) induced the highest (4 nkat ml(-1)) P-mannosidase activity. Although the fungus grew very well on mannose at an initial concentration of 20 g l(-1) there was practically no enzyme synthesis. Low level of enzyme synthesis occurred only when mannose had dropped to about 1 g l(-1). The beta-mannosidase was purified to apparent homogeneity by ethanol precipitation, differential solubility at pH 4.0 and cation ion exchange chromatography. The enzyme had a molecular mass of 99.9 kDa and a pI value of 4.8. The beta-mannosidase showed maximum activity at pH 2.5-3.0 and 76 degrees C. It exhibited highest pH stability at 5.9 after 5 h incubation at 50 degrees C. It had a half-life of 10 min at 76 degrees C. The K-m and V-max values for p-nitrophenyl-beta-D-mannopyranoside (p-NP-beta-NIP) were 1.1 mM and 61 nkat mg(-1), respectively. Low transglycosylation activity was observed when the enzyme was incubated with p-NP-beta-MP as glycosyl donor and methyl-a-D-mannopyranoside as acceptor at 50 degrees C and pH 5.0 and small amounts of beta-configured methylmannobioside was formed. (c) 2006 Elsevier Inc. All rights reserved.