Zhiliang Fan1, Xiaochao Xiong2, Weihua Wu1, Takao Kasuga3, and Ruifu Zhang1. (1) Department of Biological and Agricultural Engineering, University of California, Davis, One shields Avenue,, 3016 Bainer Hall, Davis, CA 95616, (2) Department of Biological Systems Engineering, Washington State University, LJSmith 212, Pullman, WA 99164, (3) Department of Plant Pathology, University of California, One shields Ave, Davis, CA 95616
One significant obstacle impeding the large scale production of fuels and chemicals from cellulosic biomass is the lack of a low cost processing technology. The conventional biochemical platform for biorefinery involves four distinct steps: pretreatment, enzymatic hydrolysis, fermentation, and product recovery. Sugars are produced as the reactive intermediate for the subsequent fermentation. Steps involved with overcoming the recalcitrance of cellulosic biomass (pretreatment and enzymatic hydrolysis) are the two most costly steps in the whole process. Here we propose a novel biochemical platform for fuels and chemical production that will replace the two most costly steps in the conventional platform with a single biological step. Cellulolytic microorganism(s) that can secrete all the enzymes needed to hydrolyze cellulose and hemicellulose in spite of the presence of lignin will be modified to convert most of the carbohydrate contained in the cellulosic biomass to sugar aldonates. In a second step, sugar aldonates will be utilized as the carbon source to produce ethanol and other products. The new platform can potentially lower the cost of cellulosic bioprocessing substantially. Factors contributed to the cost reduction include elimination of the high capital cost and high operating cost associated with thermo-chemical pretreatment process, consolidation of the process, and reduction of the product recovery cost due to higher ethanol concentrations produced in the fermentation step. Feasibility study has demonstrated that sugar aldonates can be produced from modified Neurospora crassa under simulated conditions; and sugar aldonates can be converted to ethanol at high efficiency and at high yields by fermentation.
