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Bacillus licheniformis BL1 was used as a starting strain to construct the recombinant tetramethylpyrazine (TMP)-producing strains by over-expression of the α-acetolactate decarboxylase gene (aldC) and α-acetolactate synthase gene (alsS), named BLC, BLS and BLCS, respectively. Then the addition of acetaldehyde was use to enhance the TMP yield in the fermentation process. During microaerobic fermentation, the aldC-overexpressed BLC strain produced 43.75 g TMP/L which was 15.47% higher than the TMP in culture yielded using the initial BL1 strain. Furthermore, the acetoin yield as TMP precursor similarly rose by 23.06% in BLC recombinant strain. In contrast, the 2,3-BD increased by 23.2% in the recombinant BLCS. TMP produced by BL1 could be bolstered via the supplementation of the acetaldehyde in fermentation medium. This method also has the same effect on the BLC strain.

UDP-xylose (UDP-Xyl) is the Xyl donor used in the synthesis of major plant cell-wall polysaccharides such as xylan (as a backbone-chain monosaccharide) and xyloglucan (as a branching monosaccharide). The biosynthesis of UDP-Xyl from UDP-glucuronic acid (UDP-GlcA) is irreversibly catalyzed by UDP-glucuronic acid decarboxylase (UXS). Until now, little has been known about the physiological roles of UXS in plants. Here, we report that AtUXS1, AtUXS2, and AtUXS4 are located in the Golgi apparatus whereas AtUXS3, AtUXS5, and AtUXS6 are located in the cytosol. Although all six single AtUXS T-DNA mutants and the uxs1 usx2 uxs4 triple mutant show no obvious phenotype, the uxs3 uxs5 uxs6 triple mutant has an irregular xylem phenotype. Monosaccharide analysis showed that Xyl levels decreased in uxs3 uxs5 uxs6 and linkage analysis confirmed that the xylan content in uxs3 xus5 uxs6 declined, indicating that UDP-Xyl from cytosol AtUXS participates in xylan synthesis. Gel-permeation chromatography showed that the molecular weight of non-cellulosic polysaccharides in the triple mutants, mainly composed of xylans, is lower than that in the wild type, suggesting an effect on the elongation of the xylan backbone. Upon saccharification treatment stems of the uxs3 uxs5 uxs6 triple mutants released monosaccharides with a higher efficiency than those of the wild type. Taken together, our results indicate that the cytosol UXS plays a more important role than the Golgi-localized UXS in xylan biosynthesis., (Copyright © 2016 The Author. Published by Elsevier Inc. All rights reserved.)