Engineering nonphosphorylative metabolism to synthesize mesaconate from lignocellulosic sugars in Escherichia coli

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.