Abstract

Mannanase production by a wild-type Aspergillus niger, isolated from spontaneously-degrading wood from South Western Nigeria was monitored at three day intervals for a period of 15 days in media containing pretreated wood shavings of Anogeissus leiocarpus, Gmelina arborea and Terminalia superba as carbon sources. Highest mannanase activity of 25.938 U/g of dry wood shavings was obtained on the 9^th day in a medium containing G. arborea as sole carbon source. Maximum activity value for the medium containing A. leiocarpus was 14.110 U/g obtained on the 9th day. On the medium containing T. superba, a maximum activity value of 10.148 U/g was obtained on the 12th day of incubation. G. arborea substrate gave the highest total protein yield of 18.146 mg/ml and the specific mannanase activity of 1.201 U/mg on the crude enzyme extracts. A mannanase activity of 19.091 U/mg was subsequently achieved after purification on ion exchange chromatography with a purification fold of 15.894. Enzyme activities were at their peaks at pH 5.5 (0.4331 U/ml) and at temperature 30°C (1.8617 U/ml). A K_m value of 0.754 mg/ml and V_max value of 1.364 U/mg/min was achieved for the enzyme which was thermally stable up to 65°C. G. arborea wood shavings hold tremendous potential in mannanase production for several industrial uses by the fungus.

Key words: Aspergillus niger, enzyme characterisation, Gmelina arborea, mannanase, solid state fermentation, purification