Substract and temperature effect on xylanase production by aspergillus fumigatus using low cost agricultural wastes / Efeito da temperatura e do substrato na produção de xilanase por aspergillus fumigatus utilizando resíduos agroindustriais de baixo custo

This study reports the optimization of xylanase production under solid state fermentation (SSF) by a thermotolerant Aspergillus fumigatus strain (SCB4) isolated from sugarcane bagasse piles of Brazilian Cerrado. Different combinations of low-cost agricultural byproducts in SSF were evaluated: sugarcane bagasse and wheat bran (1:1), sugarcane bagasse and corn straw (1:1) and only sugarcane bagasse. The enzyme biosynthesis by SSF was carried out at different temperatures (40, 45, 50 and 55 oC). The maximum levels of xylanase activity were obtained after 24 h at 45 °C using a culture medium containing sugarcane bagasse and wheat bran (1:1). Under optimal conditions, the fungal culture produced 574 U g-1 of xylanase (units/g of dry substrate). The crude enzyme showed optimal activity at 60 °C and pH 4.5. It exhibited thermostability up to 55 °C, wide range of pH stability and tolerance to ethanol, xylose and glucose. The physicochemical properties shown by this enzyme are appropriate for its application in hydrolysis of lignocellulosic residues for ethanol production and other bioproducts.

Este estudo descreve a otimização da produção de xilanase por fermentação em estado sólido (FES) por uma linhagem termotolerante de Aspergillus fumigatus isolada de pilhas de bagaço de cana-de-açúcar do Cerrado Brasileiro (linhagem SCB4). Combinações de diferentes subprodutos agrícolas de baixo custo foram avaliadas como substratos na FES: bagaço de cana-de-açúcar e farelo de trigo (1:1), bagaço de cana-de-açúcar e palha de milho (1:1) e somente bagaço de cana-de-açúcar. A produção da enzima por FES foi realizada em diferentes temperaturas (40, 45, 50 e 55 oC). Níveis máximos de xilanase (574 U g-1 de substrato seco) foram obtidos após 24 h a 45 °C, utilizando bagaço de cana-de-açúcar e farelo de trigo (1:1) no meio de cultura. O extrato enzimático bruto apresentou atividades ótimas a 60 °C e pH 4,5. A enzima exibiu estabilidade térmica até 55 °C, ampla faixa de pH de estabilidade e tolerância ao etanol, xilose e glucose. Tais propriedades físico-químicas indicam que o extrato enzimático obtido é apropriado para aplicação na hidrólise de resíduos lignocelulósicos para a produção de etanol e outros bioprodutos.

Thermotolerant and mesophylic fungi from sugarcane bagasse and their prospection for biomass-degrading enzyme production

Nineteen fungi and seven yeast strains were isolated from sugarcane bagasse piles from an alcohol plant located at Brazilian Cerrado and identified up to species level on the basis of the gene sequencing of 5.8S-ITS and 26S ribosomal DNA regions. Four species were identified: Kluyveromyces marxianus, Aspergillus niger, Aspergillus sydowii and Aspergillus fumigatus, and the isolates were screened for the production of key enzymes in the saccharification of lignocellulosic material. Among them, three strains were selected as good producers of hemicellulolitic enzymes: A. niger (SBCM3), A. sydowii (SBCM7) and A. fumigatus (SBC4). The best β-xylosidase producer was A. niger SBCM3 strain. This crude enzyme presented optimal activity at pH 3.5 and 55 °C (141 U/g). For β-glucosidase and xylanase the best producer was A. fumigatus SBC4 strain, whose enzymes presented maximum activity at 60 °C and pH 3.5 (54 U/g) and 4.0 (573 U/g), respectively. All these crude enzymes presented stability around pH 3.0–8.0 and up to 60 °C, which can be very useful in industrial processes that work at high temperatures and low pHs. These enzymes also exhibited moderate tolerance to ethanol and the sugars glucose and xylose. These similar characteristics among these fungal crude enzymes suggest that they can be used synergistically in cocktails in future studies of biomass conversion with potential application in several biotechnological sectors.