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The bioconversion of lignocellulosic biomass into value-added products provides an alternative solution to environmental and economic challenges. Nonphosphorylative metabolism can convert pentoses and d-galacturonate into 2-oxoglutarate (2-KG) in a few steps, facilitating the production of 2-KG derivatives. However, the efficiency of the Weimberg pathway from Caulobacter crescentus , a type of nonphosphorylative metabolism, is constrained by the low activity of CcXylX, 2-keto-3-deoxy-d-xylonate dehydratase. To overcome this limitation, we engineered CcXylX through directed evolution. A resulting CcXylX mutant exhibited a 3-fold higher k cat value and notably enhanced the production of 2-KG derivatives from d-xylose, a major component of lignocellulosic hydrolysates, including a 32% increase in l-glutamate titer (8.3 g/L) and a 79% increase in l-proline titer (4.3 g/L) compared with the wild-type CcXylX. This research holds promise for advancing lignocellulosic biotechnology and provides insights into economically viable production of other 2-KG derivatives besides l-glutamate and l-proline.

The D-xylose oxidative pathway (XOP) has recently been employed in several recombinant microorganisms for growth or for the production of several valuable compounds. The XOP is initiated by D-xylose oxidation to D-xylonolactone, which is then hydrolyzed into D-xylonic acid. D-Xylonic acid is then dehydrated to form 2-keto-3-deoxy-D-xylonic acid, which may be further dehydrated then oxidized into α-ketoglutarate or undergo aldol cleavage to form pyruvate and glycolaldehyde. This review introduces a brief discussion about XOP and its discovery in bacteria and archaea, such as Caulobacter crescentus and Haloferax volcanii. Furthermore, the current advances in the metabolic engineering of recombinant strains employing the XOP are discussed. This includes utilization of XOP for the production of diols, triols, and short-chain organic acids in Escherichia coli, Saccharomyces cerevisiae, and Corynebacterium glutamicum. Improving the D-xylose uptake, growth yields, and product titer through several metabolic engineering techniques bring some of these recombinant strains close to industrial viability. However, more developments are still needed to optimize the XOP pathway in the host strains, particularly in the minimization of by-product formation. [ABSTRACT FROM AUTHOR]

Production of chemicals via fermentation has been evolving over the past 30 years in search of economically viable systems. Thus far, there have been few industrially relevant chemicals that have seen commercialization, examples being lactic acid and ethanol. Currently, many of these fermentation processes still compete with food sources. In order to reduce this competition fermentation of alternative feedstocks, such as lignocellulosic biomass must to be utilized. Hemicellulosic sugars can be employed effectively for the production of chemicals by incorporating nonphosphorylative metabolism. This review covers nonphosphorylative metabolism, the pathways and enzymes involved, as well as the products that have been produced using nonphosphorylative metabolism.

Production of chemicals via fermentation has been evolving over the past 30 years in search of economically viable systems. Thus far, there have been few industrially relevant chemicals that have seen commercialization, examples being lactic acid and ethanol. Currently,many of these fermentation processes still compete with food sources. In order to reduce this competition fermentation of alternative feedstocks, such as lignocellulosic biomass must to be utilized. Hemicellulosic sugars can be employed effectively for the production of chemicals by incorporating nonphosphorylative metabolism. This review covers nonphosphorylative metabolism, the pathways and enzymes involved, as well as the products that have been produced using nonphosphorylative metabolism. [ABSTRACT FROM AUTHOR]

Dicarboxylic acids are attractive biosynthetic targets due to their broad applications and their challenging manufacturing process from fossil fuel feedstock. Mesaconate is a branched, unsaturated dicarboxylic acid that can be used as a co-monomer to produce hydrogels and fire-retardant materials. In this study, we engineered nonphosphorylative metabolism to produce mesaconate from d -xylose and l -arabinose. This nonphosphorylative metabolism is orthogonal to the intrinsic pentose metabolism in Escherichia coli and has fewer enzymatic steps and a higher theoretical yield to TCA cycle intermediates than the pentose phosphate pathway. Here mesaconate production was enabled from the d -xylose pathway and the l -arabinose pathway. To enhance the transportation of d -xylose and l -arabinose, pentose transporters were examined. We identified the pentose/proton symporter, AraE, as the most effective transporter for both d -xylose and l -arabinose in mesaconate production process. Further production optimization was achieved by operon screening and metabolic engineering. These efforts led to the engineered strains that produced 12.5 g/l and 13.2 g/l mesaconate after 48 h from 20 g/l of d -xylose and l -arabinose, respectively. Finally, the engineered strain overexpressing both l -arabinose and d -xylose operons produced 14.7 g/l mesaconate from a 1:1 d -xylose and l -arabinose mixture with a yield of 85% of the theoretical maximum. (0.87 g/g). This work demonstrates an effective system that converts pentoses into a value-added chemical, mesaconate, with promising titer, rate, and yield. [ABSTRACT FROM AUTHOR]