Fungos microaerobios na bioconversão de material lignocelulosico

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

Cellulose accounts for the major part of lignocellulose found in nature, and consequently, its degradation is essential for the operation of the global carbon cycle. Lignocellulose, such as wood, is mainly composed of a mixture of cellulose (40%), hemicellulose (20-30%), and lignin (15-30%). An association of enzymes acting in a concerted fashion degrades cellulose. This cellulase enzyme system consists of three major components, which are referred to as endoglucanase (carboximethylcellulase), exoglucanase (avicelase), and cellobiase (beta-glucosidase). These enzymatic components act synergistically in the hydrolysis of crystalline cellulose. The process by which the microorganisms degrade lignin is oxidative, involving enzymes such as lignin peroxidase, manganese peroxidase, and laccase. Cellulolytic microorganisms are found among various taxonomic groups. They include fungi and bacteria, aerobes and anaerobes, mesophiles and thermophiles and occupy a variety of habitats. Only a few groups of microorganisms are capable of degrading the complex lignin polymers and the white-rot fungi, which cause the greatest degree of mineralization, best exemplify them. Most of the lignocelluloses in nature are oxidized to carbon dioxide by aerobic microorganisms, but a substantial amount is degraded in anaerobic environments such as soil and mud that contain plant material. To verify the microbial capacity to degrade lignocellulosic material under microaerophilic conditions, seven strains were studied and three were selected: Geotríchum terrestre, Fusarium oxysporum and H2 strain (basidiomycete). The results obtained with strains H2, F. oxysporum and G. terrestre suggest that they prefer lower oxygen concentratioris for growth and enzyme production. Lignocellulolytic activities were detected in ali strains but varied with the carbon source used. The highest levels of these activities were produced by strains after growth in the complement media (addition of Tween 80, MnO2, without cystein), when compared with the result obtained after growth in nutrient media. The results obtained in this study showed that Tween 80 influences the enzymatic activity, due to better enzyme production. Ethanol and other non-gaseous fermentation products were detected following HPLC analysis. Strain H2 showed a greater production of ethanol and G. terrestre of citrate, tartarate, lactate and acetate. Since they produce enzymes necessary for the breakdown of lignocellulosic materiais and utilize most of the degradation products for growth, these strains show great potential for novel biotechnological applications

ASSUNTO(S)

fermentação enzimas biodegradação fungos lignocelulose

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