Synthetic pathway optimization for improved 1,2,4-butanetriol production.

1,2,4-Butanetriol (BT) is an important non-natural chemical with a variety of industrial applications. Identifying the bottlenecks for BT biosynthesis is expected to contribute to improving the efficiency of this process. In this work, we first constructed a prototype strain for BT production by assembling a four-step synthetic pathway and disrupting the competing pathways for xylose in Escherichia coli BW25113. Using this prototype strain, we conducted systematic fine-tuning of the pathway enzyme expression level to identify the potential bottlenecks and optimize the BT biosynthesis. Production conditions were also optimized by exploring the effects of temperature, pH and cell density on BT titer. BT production was increased by 4.3-fold from the prototype strain, achieved a final titer of 1.58 g/L with a yield of 7.9% after 72-h biotransformation.