[Optimization of 1,2,4-butanetriol synthetic pathway in Escherichia coli]

1,2,4-Butanetriol (BT) is an important non-natural chemical with a variety of industrial applications. A recombinant Escherichia coli biosynthesizing BT from D-xylose was constructed by heterologously expressing xdh and mdlC, and knocking out competing pathway genes including xylA, xylB, yjhE, yagH and ycdW. To optimize BT synthesis pathway, the third catalytic step that catalyzes the decarboxylation reaction of 3-deoxy-D-glycero-pentulosonic acid was identified as a potential bottleneck. Consequently, 2-keto acid decarboxylases from three different microorganisms were screened, and the kivD gene from Lactococcus lactis was found to increase BT titer by 191%. The improved strain BW-025 reached a final BT titer of 2.38 g/L under optimized transformation conditions. Attempts on synthetic pathway optimization were also made by fine-tuning the expression levels of each enzyme involved in the whole pathway based on BW-025. As a result, an xdh overexpressed recombinant strain, BW-074 was finally generated, with 48.62% higher BT production than that of BW-025.