Pretreatment and Detoxification of Acid-Treated Wood Hydrolysates for Pyruvate Production by an Engineered Consortium of
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Pretreatment and Detoxification of Acid-Treated Wood Hydrolysates for Pyruvate Production by an Engineered Consortium of Escherichia coli Hemshikha Rajpurohit 1 & Mark A. Eiteman 1 Received: 18 February 2020 / Accepted: 23 April 2020/ # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
The biorefinery concept makes use of renewable lignocellulosic biomass to produce commodities sustainably. A synthetic microbial consortium can enable the simultaneous utilization of sugars such as glucose and xylose to produce biochemicals, where each consortium member converts one sugar into the target product. In this study, woody biomass was used to generate glucose and xylose after pretreatment with 20% (w/v) sulfuric acid and 60-min reaction time. We compared several strategies for detoxification with charcoal and sodium borohydride treatments to improve the fermentability of this hydrolysate in a defined medium for the production of the growth-associated product pyruvate. In shake flask culture, the highest pyruvate yield on xylose of 0.8 g/g was found using pH 6 charcoal-treated hydrolysate. In bioreactor studies, a consortium of two engineered E. coli strains converted the mixture of glucose and xylose in batch studies to 12.8 ± 2.7 g/L pyruvate in 13 h. These results demonstrate that lignocellulosic biomass as the sole carbon source can be used to produce growth-related products after employing suitable detoxification strategies. Keywords Bioprocess . Fermentation . Lignocellulose . Microbial consortium . Pyruvic acid
Introduction The demand of sustainable products from the renewable materials is increasing as a consequence of depletion of fossil fuels and concerns for climate change [1]. Lignocellulosic sources such as forest biomass, energy crops, and food and agricultural residues are potential feedstocks to produce biochemicals in a biorefinery [2, 3]. To release five- and six-carbon sugar monomers from lignocellulosic biomass, several pretreatment strategies have been employed
* Mark A. Eiteman [email protected]
1
School of Chemical, Material and Biomedical Engineering, University of Georgia, Athens, GA 30602, USA
Applied Biochemistry and Biotechnology
including mineral acid, alkaline, microwave, and steam explosion [4]. Although the low cost of sulfuric acid makes it a conventional method for pretreatment, acid hydrolysis of lignocellulose generates microbial inhibitors such as furans, phenolics, and organic acids [5]. Many physical, chemical, and biological detoxification strategies have been proposed to remove inhibitors from the hydrolysate and enhance the generation of a microbial product. For example, activated charcoal has improved the bioproduction of ethanol [6–8], xylitol [9–11], or succinic acid [12–14]. Direct addition of reducing agents including sodium borohydride or sodium dithionite also improves ethanol generation from lignocellulosic hydrolysate [15, 16]. Combining detoxification strategies can further enhance the fermentability of acid-treated biomass [17, 18]. F
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