Abstract
Basidiomycetes are laccase producers used for hydrolysis of lignocellulosic byproducts in fermentative processes and could be used on biofuel production or ruminant feeding. The objective of this study was to evaluate the effect of concentrations of non-protein nitrogen sources on laccase production and mycelial growth of Pleurotus ostreatus, Lentinula edodes and Agaricus blazei. The fungi were grown on soybean hulls to which urea (U), ammonium sulfate (AS) or mixture of AS:U (1:1) were added to achieve carbon/nitrogen (C/N) ratios of 5, 15, 20 or 30. The average longitudinal mycelial growth was measured and laccase activity was determined by the oxidation of 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid. Higher C/N ratios increased mycelial growth and decreased laccase production. The highest activities were obtained with a C/N ratio of 5. P. ostreatus, L. edodes and A. blazei produced more laccase when AS, AS:U and U, respectively, were added. In addition, C/N ratios lower than 30 induced laccase syntheses, inhibited mycelial growth and were a better condition for pre-hydrolysis of plant residues.
Highlights
In 2008, Brazil produced approximately 60 million tons of soybean (Glycine max) (IBGE, 2008) and 1.2 million ton of soybean hull, which contains 66-69% of neutral detergent fiber and 3-8% of lignin (Zambom et al, 2001)
The objective of this study was to evaluate the effect of concentrations of non-protein nitrogen sources on laccase production and mycelial growth of Pleurotus ostreatus, Lentinula edodes and Agaricus blazei
For each fungus the results obtained for mycelial growth and laccase production were characterized by very low standard deviations among experimental replicates (Figures 1 to 6)
Summary
In 2008, Brazil produced approximately 60 million tons of soybean (Glycine max) (IBGE, 2008) and 1.2 million ton of soybean hull, which contains 66-69% of neutral detergent fiber and 3-8% of lignin (Zambom et al, 2001). Laccase enzyme has been used for previous lignin degradation in order to increase cellulose exposure to fungal cellulases (Anderson et al, 1988). Fungal enzyme synthesis is strongly influenced by the strain, substrate composition and nitrogen concentration in the cultivation medium (Elisashvili et al, 2008; Elisashvili and Kachlishvili, 2009; Staji et al, 2006). The carbon/nitrogen (C/N) ratio is one of the most important factors to balance biomass and biocomposite productions. The excess or lack of nitrogen content in the substrate may be a limiting factor for fungus
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