Submitted to: Institution of Chemical Engineers Transactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/19/2005
Publication Date: 6/15/2006
Citation: Qureshi, N., Dien, B.S., Nichols, N.N., Saha, B.C., Cotta, M.A. 2006. Genetically engineered Escherichia coli for ethanol production from xylose: substrate and product inhibition and kinetic parameters. Institution of Chemical Engineers Transactions. 84(2):114-122. Interpretive Summary: In this article, ethanol production from xylose (a component of wood sugar) was studied using genetically engineered culture Escherichia coli. This culture is capable of producing ethanol from wood sugars (hexoses and pentoses) derived from wood, corn fiber, wheat straw, rice straw, and other agricultural residues. Successful biological conversion of both the wood sugars [hexoses (glucose, mannose, etc.) and pentoses (xylose, arabinose, etc.)] to ethanol would make ethanol production from agricultural residues economically attractive. Currently, approximately 2.84 billion gallons of ethanol are produced from corn and are expected to increase to 5 billion gallons by 2020. Further increase in ethanol production would necessitate use of agricultural residues in addition to corn. During these investigations, we characterized ethanol production from xylose by E. coli and found that the process could further be improved if simultaneous production and recovery of ethanol are combined into a single process. These developments will make ethanol production from agricultural residues economically attractive. This technology will benefit U.S. farmers, ethanol industry, automobile industry, and the public.
Technical Abstract: A recombinant strain of Escherichia coli FBR5 was characterized for ethanol production from xylose in batch reactors. Up to a salt (NaCl) concentration of 10 gL**-1, the culture exhibited no inhibition. Above 10 gL**-1 of salt concentration, the culture experienced inhibition, and the maximum concentration of salt that E. coli FBR5 could tolerate was 40 gL**-1. At 40 gL**-1 NaCl concentration, the value of umax was reduced by a factor of 5. The culture could tolerate a maximum xylose concentration of 250 gL**-1; however, at that concentration a reduced cell growth was obtained. A maximum cell concentration of 0.30 gL**-1 was obtained at this sugar concentration as compared to 0.75 gL**-1 at 100 gL**-1 initial xylose. As the concentration of xylose increased, ethanol specific productivity (v) decreased from 0.98 to 0.70 h**-1. In these experiments, a maximum yield of 0.50 (g ethanol g**-1 xylose) was achieved with a productivity of 0.73 gL**-1h**-1. Ethanol inhibition studies suggested that the maximum tolerance of the culture was 50 gL**-1 ethanol. However, the maximum ethanol that could be produced was 43.5 gL**-1. In pH controlled experiments, the maximum ethanol productivity of 0.90 gL**-1h**-1 was obtained. The value of Km (Michaelis-Menten constant) was evaluated to be 4.38 gL**-1.