Genetically engineered Escherichia coli FBR5: Part II. Ethanol production from xylose and simultaneous product recovery

Authors: Qureshi, Nasib; Dien, Bruce; Liu, Siqing; Saha, Badal; Cotta, Michael; Hughes, Stephen; Hector, Ronald - Ron

Submitted to: Biotechnology Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2012
Publication Date: 10/11/2012
Citation: Qureshi, N., Dien, B.S., Liu, S., Saha, B.C., Cotta, M.A., Hughes, S.R., Hector, R.E. 2012. Genetically engineered Escherichia coli FBR5: Part II. Ethanol production from xylose and simultaneous product recovery. Biotechnology Progress. 28(5):1179-1185.

Interpretive Summary: Cost effective production of fuel ethanol from agricultural residues such as corn stover requires the use of both pentose and hexose sugars contained in these feedstocks. In this research the pentose sugar xylose was used to produce ethanol and improve process economics. In a traditional batch process dilute sugar solutions are used resulting on low ethanol product yields. This low ethanol yield results in increased process volumes and increased plant costs thus making the process of ethanol production uneconomical. Concentrating the sugar solution could increase yield but the resulting higher ethanol concentration starts killing the microbial culture that produces the ethanol, thus halting the process. The simultaneous removal of ethanol during fermentation could reduce this toxicity. To pursue this goal, concentrated residue sugar solution was used and toxic ethanol was recovered simultaneously thus improving process efficiency 2.2 fold. It is anticipated that such a process would benefit fuel ethanol process economics and hence the US farmers, the biofuels industry, and the US public.

Technical Abstract: In these studies concentrated xylose solution was fermented to ethanol employing Escherichia coli FBR5 which can ferment both lignocellulosic sugars (hexoses and pentoses). E. coli FBR5 can produce 40-50 gL-1 ethanol from 100 gL-1 xylose in batch reactors. Increasing sugar concentration beyond this level results in the loss of sugar with the reactor effluent thus affecting the process yield adversely. In a non-integrated system without simultaneous product removal more than 120 gL-1 xylose was left unused of the 220 gL-1 that was fed into the reactor. In contrast to this, application of simultaneous product removal by gas stripping was able to relieve product inhibition and the culture was able to utilize 216.6 gL-1 xylose thus producing 140 gL-1 (based on reactor volume) ethanol resulting in a product yield of 0.48. The product stream achieved an ethanol concentration up to 148.41 gL-1. This process has potential for greatly improving the performance of E. coli FBR5 where the strain can ferment all the lignocellulosic sugars to ethanol and gas stripping can be applied to recover product.