Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2012
Publication Date: 2/23/2012
Publication URL: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0031693
Citation: Ziliang, F., Weihua, W., Hildebrand, A., Kasuga, T., Zhang, R., Xiaochao, X. 2012. A novel biochemical platform for fuels and chemicals production from cellulosic biomass. PLoS One. 7(2). Interpretive Summary: Cellulosic biomass is a sustainable source for organic fuels, chemicals, and materials; and is available at low cost and in large abundance. The central obstacle impeding the widespread utilization of cellulosic biomass is the absence of a low-cost processing technology. One strategy to reduce the processing cost is through process consolidation. We propose a novel biochemical platform for fuels and chemical production, which combines the three most expensive steps: pretreatment, cellulase production, and enzymatic hydrolysis into a single biological step and produces sugar aldonates instead of sugars as the reactive intermediates.
Technical Abstract: The conventional biochemical platform for biofuels production featuring enzymatic hydrolysis involves five key steps: pretreatment, cellulase production, enzymatic hydrolysis, fermentation, and product recovery. Sugars are produced as reactive intermediates for subsequent fermentation to fuels and chemicals. Herein, an alternative biochemical platform is proposed. Pretreatment, enzymatic hydrolysis, and cellulase production is consolidated into one single step, referred to as consolidated aerobic processing, and sugar aldonates are produced as the reactive intermediates for biofuels production by fermentation. In this study, we investigated the primary feasibility of the proposed platform using Neurospora crassa as the model microorganism and the conversion of cellulose to ethanol as the model system. We intended to prove the two hypotheses: 1) cellulose can be directed to produce cellobionate by reducing '-glucosidase production and by enhancing cellobiose dehydrogenase production; and 2) cellobionate can be utilized as a carbon source for ethanol and other chemical production, which lay the foundation of the proposed new platform. Our results showed that knocking out multiple copies of '-glucosidase led to cellobionate production from cellulose, without jeopardizing the cellulose hydrolysis rate. Simulating CDH over-expression by addition of exogenous CDH led to more cellobionate production. Gluconate was metabolized by an ethanologen Escherichia coli KO11 for ethanol production at a high yield and at a rate even faster than that of glucose. Glucose and gluconate was utilized simultaneously in glucose and gluconate co-fermentation.