Enhancement of xylose utilization from corn stover by a recombinant bacterium for ethanol production

Authors: Saha, Badal; Qureshi, Nasib; Kennedy, Gregory - Greg; Cotta, Michael

Submitted to: Bioresource Technology
Publication Type: Abstract Only
Publication Acceptance Date: 5/30/2015
Publication Date: 6/2/2015
Publication URL: http://www.sciencedirect.com/science/article/pii/S0960852415006057
Citation: Saha, B.C., Qureshi, N., Kennedy, G.J., Cotta, M.A. 2015. Enhancement of xylose utilization from corn stover by a recombinant bacterium for ethanol production [abstract]. American Society for Microbiology. 190:182-188

Interpretive Summary:

Technical Abstract: Recombinant ethanologenic Escherichia coli ferments glucose, xylose and arabinose to ethanol. However, the bacterium preferentially utilizes glucose first, then arabinose and finally xylose (sequential utilization of sugars) during fermentation of lignocellulosic hydrolyzates to ethanol making the process slower. Recombinant E. coli FBR5 was used. Corn stover (CS, 10%, w/v) was pretreated with H2SO4 (0.75%, v/v; 160 oC, 0 min holding time) which allowed the release of maximum sugars upon enzymatic hydrolysis while minimizing the generation of fermentation inhibitors (furfural and hydroxymethyl furfural). The pretreated CS was enzymatically saccharified at pH 5.0 and 45 oC for 72 h using a cocktail of cellulase and ß-glucosidase preparations. The fermentation of this hydrolyzate was carried out in pH-controlled 250 ml fleakers with a working volume of 200 ml at pH 6.5 and 35 oC. Simultaneous saccharification and fermentation (SSF) experiments were carried out in DasGip Parallel Bioreactor systems using 250 ml bioreactors with a working volume of 200 ml at 35 oC. Effects of substrate-selective inoculum prepared by growing on 2% (w/v) glucose, xylose, arabinose, GXA (glucose, xylose, arabinose, 1:1:1) and 3 times diluted CS hydrolyzate (dilute acid pretreated and enzymatically hydrolyzed, CSH) on ethanol production from CSH by a mixed sugar utilizing recombinant Escherichia coli (strain FBR5) were investigated. The ethanol productivity was faster for the seed grown on xylose followed by GXA, CSH, glucose and arabinose. Arabinose grown seed performed slower than other seeds. Using xylose-grown inoculum, delayed addition of enzyme cocktail in SSF of dilute acid pretreated CS by recombinant E. coli FBR5 allowed the fermentation to finish in shorter time than adding the enzymes along with the seed inoculum. Use of substrate selective inoculum and fermenting pentose sugars first under glucose limited condition helped to alleviate the catabolite repression of the recombinant bacterium for ethanol production from lignocellulosic hydrolyzate. This research demonstrates that the catabolite repression effects of glucose and arabinose on xylose utilization by the recombinant bacterium for ethanol production can be alleviated by using substrate selective inoculum and fermenting xylose and arabinose first under glucose limited condition.