Simultaneous production of high activities of thermostable endoglucanase and β-glucosidase by the wild thermophilic fungus Thermoascus aurantiacus

Abstract

The culture-medium composition was optimised, on a shake-flask scale, for simultaneous production of high activities of endoglucanase and beta-glucosidase by Thermoascus aurantiacus using statistical factorial designs. The optimised medium containing 40.2 g l(-1) Solka Floc as the carbon source and 9 g l(-1) soymeal as the organic nitrogen source yielded 1130 nkat ml(-1) endoglucanase and 116 nkat ml(-1) beta-glucosidase activities after 264 h as shake cultures. In addition, good levels of beta-xylanase (3479 nkat ml(-1)) and low levels of filter-paper cellulase, beta-xylosidase, alpha-L-arabinofuranosidase, beta-mannanase, beta-mannosidase, alpha-galactosidase and beta-galactosidase were detected. Batch fermentation in a 5-1 laboratory fermentor using the optimised medium allowed the production of 940 nkat ml(-1) endoglucanase and 102 nkat ml(-1) beta-glucosidase in 192 h. Endoglucanase and beta-glucosidase showed optimum activity at pH 4.5 and pH 5, respectively, and they displayed optimum activity at 75 degrees C. Endoglucanase and beta-glucosidase showed good stability at pH values 4-8 and 4-7, respectively, after a prolonged incubation (48 h at 50 degrees C). Endoglucanase had half-lives of 98 h at 70 degrees C and 4.1 h at 75 degrees C, while beta-glucosidase had half-lives of 23.5 h at 70 degrees C and 1.7 h at 75 degrees C. Alkali-treated bagasse, steam-treated wheat straw, Solka floc and Sigmacell 50 were 66, 48.5, 33.5 and 14.4% hydrolysed by a crude enzyme complex of T. aurantiacus in 50 h.

Production of xylanase and CMCase on solid state fermentation in different residues by Thermoascus aurantiacus miehe

“…The optimum temperature of the CMCase was 75ºC and at 85ºC the crude enzyme still had 60% of the original activity. The optimum temperature found for the CMCase is in good agreement with the reports for the other T. aurantiacus strains (9,14). Effect of the temperature in the stability of crude enzymes is shown in the Fig.…”

“…However in pH 4.0 the activity was almost completely lost and in pH 7.0 the enzyme still retained 58% of its activity. The optimum pH found for the CMCase is comparable to those for the other T aurantiacus strains (9,27). Results presented in Fig.…”

“…Different strains of the Thermoascus aurantiacus fungus have been reported to be good producers of thermostable endoglucanase and/or xylanase (8)(9)(10)(13)(14)(15)(16)22,(24)(25)(26), however there are few accounts of simultaneous production of CMCase and xylanase by this fungus on solid state fermentation.…”

Use of a Mixture of Thermophilic Enzymes Produced by the Fungus <i>Thermoascus aurantiacus</i> to Enhance the Enzymatic Hydrolysis of the Sugarcane Bagasse Cellulose

“…T. aurantiacus is specially a good producer of β-glucosidases. In general, its β-glucosidases show high stability, half lives at 70°C of 23.5 h (Gomes et al, 2000), optimum temperature and pH between 65 and 80°C and 4.5 and 6, respectively (Gomes et al, 2000;Hong et al, 2007). Different T. aurantiacus strains show endoglucanases with acid pI (around 3.5-3.7) (Hong et al, 2007;Parry et al, 2001) that display high stability (at 70°C half live of 98 h) (Gomes et al, 2000), optimum temperature and pH between 65 and 80°C and 4.0 and 5.5, respectively (Parry et al, 2001;Kalogeris et al, 2003).…”

“…In general, its β-glucosidases show high stability, half lives at 70°C of 23.5 h (Gomes et al, 2000), optimum temperature and pH between 65 and 80°C and 4.5 and 6, respectively (Gomes et al, 2000;Hong et al, 2007). Different T. aurantiacus strains show endoglucanases with acid pI (around 3.5-3.7) (Hong et al, 2007;Parry et al, 2001) that display high stability (at 70°C half live of 98 h) (Gomes et al, 2000), optimum temperature and pH between 65 and 80°C and 4.0 and 5.5, respectively (Parry et al, 2001;Kalogeris et al, 2003). Besides producing cellulases, T. aurantiacus can secret most of the hemicellulolytic enzymes, endo-xylanase being the main enzyme detected in its culture, similar to several other well known hemicellulase-producing microorganisms such as Aspergillus niger (Bailey and Poutanen, 1989;Kang et al, 2004;Coral et al, 2002) and Trichoderma reesei (Juhasz et al, 2005).…”