Efficient utilization of pentoses for bioproduction of the renewable two-carbon compounds ethylene glycol and glycolate

Abstract

The development of lignocellulose as a sustainable resource for the production of fuels and chemicals will rely on technology capable of converting the raw materials into useful compounds; some such transformations can be achieved by biological processes employing engineered microorganisms. Towards the goal of valorizing the hemicellulose fraction of lignocellulose, we designed and validated a set of pathways that enable efficient utilization of pentoses for the biosynthesis of notable two-carbon products. These pathways were incorporated into Escherichia coli, and engineered strains produced ethylene glycol from various pentoses, including simultaneously from D-xylose and L-arabinose; one strain achieved the greatest reported titer of ethylene glycol, 40 g/L, from D-xylose at a yield of 0.35 g/g. The strategy was then extended to another compound, glycolate. Using D-xylose as the substrate, an engineered strain produced 40 g/L glycolate at a yield of 0.63 g/g, which is the greatest reported yield to date.

Ethylene glycol and glycolic acid production from xylonic acid by Enterobacter cloacae

“…Cell growth and the synthesis of ethylene glycol and glycolic acid were not coincided. This is different to all reports that using E. coli as the producer, in which the cell growth and ethylene glycol synthesis are coincided [3,4]. Ethylene glycol and glycolic acid synthesis was inhibited at an agitation rate of 800, but xylonic acid consumption was at a high rate, (Figure.…”

“…Furthermore, 20 g/L of ethylene glycol was produced with a molar yield of 0.38 g/g xylose and productivity of 0.37 g/L h by an modified strain of E. coli using xylulose as an intermediate [3]. In another study 40 g/L ethylene glycol was produced with a yield of 0.63 g/g xylose and productivity of 0.55 g/L h after some optimization of the conditions [4]. Using glucose as substrate, 3.5 g/L ethylene glycol was produced by engineering C. glutamicum, with a yield of 0.08 g/g glucose and productivity of 0.05 g/L h [5].…”

“…However, pyruvate produced in the process was utilized by cells. In a research that using engineered E. coli of ethylene glycol and glycolic acid production, pyruvate was partly recovered for glycolic acid synthesis and the total yield of the process was improved [4].…”

Exploring biochemical pathways for mono-ethylene glycol (MEG) synthesis from synthesis gas

“…Furthermore, the industrial process also suffers from low selectivity of MEG because higher order glycols are also produced in the process due to the increased reactivity of Ethylene oxide towards MEG than to water (Forkner et al, 2000;Rebsdat and Mayer, 2000). It is thus of interest to explore the routes for biological production of MEG from renewable feedstocks such as sugars using engineered microbial organisms, and this interest has obtained significant attention from the scientific community recently (Alkim et al, 2015;Liu et al, 2013;Pereira et al, 2016a;Pereira et al, 2016b;Stephanopoulos et al, 2013).…”

“…So far, bio-based production of MEG using engineered Escherichia coli strains has been reported from pentose and hexose sugars, including xylose (Alkim et al, 2015;Liu et al, 2013;Pereira et al, 2016a), arabinose (Pereira et al, 2016a), and glucose (Pereira et al, 2016b). These processes are very promising since the sugars are abundant in lignocellulosic biomass feedstocks obtained from agricultural wastes, forestry residues, grasses, and woody materials (Anwar et al, 2014;Menon and Rao, 2012).…”