Production of a xylose-stimulated β-glucosidase and a cellulase-free thermostable xylanase by the thermophilic fungus Humicola brevis var. thermoidea under solid state fermentation.
Humicola brevis var. thermoidea cultivated under solid state fermentation in wheat bran and water (1:2 w/v) was a good producer of β-glucosidase and xylanase. After optimization using response surface methodology the level of xylanase reached 5,791.2 ± 411.2 U g(-1), while β-glucosidase production was increased about 2.6-fold, reaching 20.7 ± 1.5 U g(-1). Cellulase levels were negligible. Biochemical characterization of H. brevis β-glucosidase and xylanase activities showed that they were stable in a wide pH range. Optimum pH for β-glucosidase and xylanase activities were 5.0 and 5.5, respectively, but the xylanase showed 80 % of maximal activity when assayed at pH 8.0. Both enzymes presented high thermal stability. The β-glucosidase maintained about 95 % of its activity after 26 h in water at 55 °C, with half-lives of 15.7 h at 60 °C and 5.1 h at 65 °C. The presence of xylose during heat treatment at 65 °C protected β-glucosidase against thermal inactivation. Xylanase maintained about 80 % of its activity after 200 h in water at 60 °C. Xylose stimulated β-glucosidase activity up to 1.7-fold, at 200 mmol L(-1). The notable features of both xylanase and β-glucosidase suggest that H. brevis crude culture extract may be useful to compose efficient enzymatic cocktails for lignocellulosic materials treatment or paper pulp biobleaching.
Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, 14040-901, Brazil. dcmasui@usp.br
Douglas Chodi
DC
Masui
Ana Lucia Ribeiro Latorre
AL
Zimbardi
Flávio Henrique Moreira
FH
Souza
Luis Henrique Souza
LH
Guimarães
Rosa Prazeres Melo
RP
Furriel
João Atílio
JA
Jorge
D001203:Ascomycota / Q000201:enzymology*; D018533:Biomass; D002480:Cellulase / Q000302:isolation & purification; D043364:Endo-1,4-beta Xylanases / Q000096:biosynthesis* / Q000378:metabolism; D004795:Enzyme Stability; D005285:Fermentation; D005656:Fungal Proteins / Q000096:biosynthesis / Q000378:metabolism; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D014994:Xylose / Q000494:pharmacology; D001617:beta-Glucosidase / Q000096:biosynthesis* / Q000378:metabolism
D005656:Fungal Proteins; D014994:Xylose; D001617:beta-Glucosidase; D002480:Cellulase; D043364:Endo-1,4-beta Xylanases