Nutrient Regulation and Combined Pretreatment Strategies to Improve the Rate of Delignification by White Rot Fungi
Date
2014-01-20
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Abstract
Delignification is necessary for efficient conversion of lignocellulosic biomass to biofuels. Microbial delignification by white rot fungi is achieved by the action of lignin degrading enzymes, laccase and peroxidase. As the microbial process of delignification is very slow, two strategies have been employed to achieve effective delignification in a short duration. In the first strategy, nutrient regulation of lignin degrading enzymes was exploited to identify the specific carbon and nitrogen sources, their ratio and inducer concentrations and to optimize the nutrients for maximum ligninolytic activity. In the second strategy, fungal delignification was combined with hydrothermal process.
A dual effect of copper on Dichomitus squalens laccase activity, inducing and suppressing was revealed. Maximum laccase activity is a function of fungi tolerance to copper and media composition. Some nutrients improved tolerance of cells and laccase-producing system to copper load. Methylated substrates in combination with casein and copper demonstrated high potential to support fungi tolerance and enhanced laccase activity.
In addition to induction, the suppression of peroxidase activity by Mn2+ (Manganese sulfate) has been observed in D. squalens and Ceriporiopsis subvermispora. The induction and suppression were independent of fungal growth, but depended on the nutritional conditions. Manipulation of carbon and nitrogen sources shifted the peroxidase suppression by Mn2+ to high concentrations and, hence, increased the peroxidase tolerance to Mn2+ and, consequently, peak peroxidase activities.
Optimized nutrient parameters from studies with the monocultures of D. squalens and C. subvermispora were used to design the experiments for co-cultivation of the above microorganisms. Cross regulations of laccase and peroxidase activities was observed for arabinose, casein, copper and manganese. Optimization resulted in the production of 1378 and 1372 U/g protein of laccase and peroxidase respectively. Crude enzyme mixture from optimized media degraded 16.9% of lignin in wheat straw.
To test the second strategy, raw wheat straw was exposed to hydrothermal process followed by fungal hydrolysis. On substrate cooling, by-products of lignin degradation via hydrothermal treatment recondensed on the cellulose fibers. The following fungi treatment enhanced lignin hydrolysis by degradation of the residual by-products. The combined approach is an effective method to prepare substrates for downstream fermentation of cellulose to biofuels.
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Engineering--Chemical
Citation
Kannaiyan, R. (2014). Nutrient Regulation and Combined Pretreatment Strategies to Improve the Rate of Delignification by White Rot Fungi (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/27152