Paper 7 _Metabolic Engineering_Transcript

Lignocellulosic biomass is found abundantly in the biosphere of earth which can be a good source for bioethanol production. The sugar polymers of cell wall like cellulose and hemicelluloses are bound with lignin, resisting their hydrolysis. Pretreatment of biomass is necessary to expose cellulose by degradation of lignin, which is a major problem in pretreatment. Saccharomyces cerevisae has been taken as the best sugar fermenter used in industry to ferment glucose based agricultural products to ethanol but Saccharomyces
cerevisiae is unable to degrade lignin. The basidiomycetes such as white rot fungi produce laccase enzyme that degrade lignin. The three copper centered metalloezyme, laccase of class oxidoreductase (EC 1.10.3.2) catalyze oxidation of lignin of lignocellulose so that lignin free hemicellulose and cellulose can be extracted. The metabolic engineering of Saccharomyces cerevisiae expressing laccase gene enables to degrade lignin. For such purposes, laccase gene from Ganoderma lucidum is most widely utilized for the heterologous expression in the Saccharomyces. The development of such yeast can degrade lignin that will reduce the cost of pretreatment. The further step for release of hexose and pentose, in this case will be the heterologous expression of cellulase and hemicellulase genes in Saccharomyces. Finally, introduction of pentose- especially xylose
utilization pathway should be extensively explored and if succeeded will be a great step
in conversion of lignocellulosic biomass in to high value ethanol fuel.

Mitesh Shrestha 7