Hydrolysis of sugarcane bagasse with enzyme preparations from Acrophialophora nainiana grown on different carbon sources

Abstract

The filamentous fungus Acrophialophora nainiana, isolated from a hot spring in Brazil, was grown in liquid culture on different cellulosic and lignocellulosic carbon sources for seven days and enzyme extracts were characterised with respect to their carbohydrase activity profile. The enzyme extracts obtained from growing A. nainiana on cellulose, dirty-cotton residue, sugarcane bagasse and banana stem were used in the hydrolysis of sugarcane bagasse untreated (UT), pre-treated by steam explosion (SET) and pre-treated by acid-catalysed steam explosion (SAT). The carbohydrase activity profile of the enzyme preparations varied significantly with the used carbon source. The highest enzyme activities, especially total cellulase (0.0132 IU) and xylanase (0.0774 IU) activities, were obtained with banana stem as the carbon source. Pectinase activity was produced on all carbon sources at comparable levels. On sugarcane bagasse, total cellulase activity on filter paper and pectinase activities were predominant, but a very low amount of xylanase and CMCase activity, 0.0011 IU and 0.0019 IU, respectively, was found. The exocellulase/endocellulase activity ratio (FPAsol/FPAinsol) of the cellulases produced varied between 1 and 4 depending on the substrate. The highest endocellulase activity (FPAinsol) content was obtained when grown on sugarcane bagasse. Conversions to reducing sugars of the differently pre-treated sugarcane bagasse substrates with enzyme preparations from A. nainiana were in general low. The highest conversion to reducing sugars (˜18%) was obtained for the SET bagasse by the banana stem enzyme preparation, while conversions with the other enzyme preparations were below 5%. In most cases a very low conversion (below 1%) was obtained for the SAT bagasse, but better conversions were achieved for the UT. These results are mainly attributable to the hydrolysis of the hemicellulose fraction and the low cellulase and β-glucosidase activities in the enzyme preparations. Hydrolysis data were also analysed and successfully fitted with a fractal kinetics model, and model parameters are discussed with respect to the carbon source used for A. nainiana enzyme production and substrate pre-treatment.