Although sugars are the primary feedstock for the biological production of renewable fuels and chemicals, recent progress in the development of organisms that accumulate bio-oils (i.e. triesters of fatty acids, FAs, and glycerol) and the abundance of glycerol- and fatty acid-rich industrial byproducts make these carbon sources an attractive alternative. In addition to abundance, the higher degree of reduction and higher metabolic efficient of glycerol and FAs can support product yields significantly higher than those obtained from sugars. However, most industrial organisms metabolize glycerol and FAs only under respiratory conditions, which do not lead to the synthesis of fermentation products. We then have used synthetic and systems biology approaches to engineer the efficient synthesis of fuels and chemicals from these substrates (references below). Several native and heterologous fermentative pathways were engineered to function in E. coli under anaerobic and microaerobic conditions. Pathways for the efficient utilization of glycerol and FAs were engineered as well. Biofuels (ethanol, butanol, and hydrogen) and biochemicals (succinate, lactate, acetate, propionate, 1,2-propanediol, acetone, and isopropanol) were chosen as representative products to illustrate the feasibility of the proposed approach. Product yields in most cases exceeded those achieved with the use of sugars, clearly demonstrating the advantages of glycerol and FAs.
- Dellomonaco et al. 2009. Synthetic respiro-fermentative metabolism for the production of fuels and chemicals from fatty acids. App Environ Microbiol (MS in Review). - Gonzalez et al. 2009. Production of ethanol from thin stillage by metabolically engineered Escherichia coli. Biotechnol Letters (DOI: 10.1007/s10529-009-0159-2). - Gupta et al. 2009. Anaerobic fermentation of glycerol in Paenibacillus macerans: metabolic pathways and environmental determinants. App Environ Microbiol 75: 5871. - Durnin, et al. 2009. Understanding and harnessing the microaerobic metabolism of glycerol in Escherichia coli. Biotechnol Bioeng 103: 148. - Yazdani and Gonzalez. 2008. Engineering Escherichia coli for the efficient conversion of glycerol to ethanol and co-products. Metab Eng 10: 340. - Gonzalez et al. 2008. A new model for the anaerobic fermentation of glycerol in enteric bacteria: trunk and auxiliary pathways in Escherichia coli. Metab Eng 10: 234. - Murarka et al. 2008. Fermentative utilization of glycerol in Escherichia coli and its implications for the production of fuels and chemicals. App Environ Microbiol 74: 1124. - Yazdani and Gonzalez. 2007. Anaerobic fermentation of glycerol: A path to economic viability for the biofuels industry. Curr Opin Biotechnol 18: 213. - Dharmadi et al. 2006. Anaerobic fermentation of glycerol by Escherichia coli: a new platform for metabolic engineering. Biotechnol Bioeng 94: 821.
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