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Solid-Liquid Equilibrium in the System 2-Keto-L-Gulonic Acid + L-Ascorbic Acid + Water.

ABSTRACT: The solid-liquid equilibrium (SLE) in the ternary system 2-keto-L-gulonic acid (HKGA) + L-ascorbic acid (vitamin?C) + water was investigated experimentally at temperatures between 276?K and 308?K at ambient pressure, i.e., under conditions that are of particular interest for industrial applications. Phase diagrams with one eutonic point were obtained for all temperatures. The dissociation constant and the solubility constant of vitamin C were determined as a function of temperature. Based on an extended version of the Debye-Hückel theory, a physicochemical model was developed that describes the SLE in the ternary system. The agreement between experimental data and results from the model is excellent.

SUBMITTER: Jirasek F

PROVIDER: S-EPMC6472595 | biostudies-literature | 2018 Dec

REPOSITORIES: biostudies-literature

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Solid-Liquid Equilibrium in the System 2-Keto-L-Gulonic Acid + L-Ascorbic Acid + Water.

Jirasek Fabian F Galeotti Nadia N Burger Jakob J Hasse Hans H

Chemical engineering & technology 20181023 12

The solid-liquid equilibrium (SLE) in the ternary system 2-keto-L-gulonic acid (HKGA) + L-ascorbic acid (vitamin C) + water was investigated experimentally at temperatures between 276 K and 308 K at ambient pressure, i.e., under conditions that are of particular interest for industrial applications. Phase diagrams with one eutonic point were obtained for all temperatures. The dissociation constant and the solubility constant of vitamin C were determined as a function of temperature ...[more]

PMID: 31007397

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Project description:Currently, the establishment of synthetic microbial consortia with rational strategies has gained extensive attention, becoming one of the important frontiers of synthetic biology. Systems biology can offer insights into the design and construction of synthetic microbial consortia. Taking the high-efficiency production of 2-keto-l-gulonic acid (2-KLG) as an example, we constructed a synthetic microbial consortium "Saccharomyces cerevisiae-Ketogulonigenium vulgare" based on systems biology analysis. In the consortium, K. vulgare was the 2-KLG producing strain, and S. cerevisiae acted as the helper strain. Comparative transcriptomic analysis was performed on an engineered S. cerevisiae (VTC2) and a wild-type S. cerevisiae BY4741. The results showed that the up-regulated genes in VTC2, compared with BY4741, were mainly involved in glycolysis, TCA cycle, purine metabolism, and biosynthesis of amino acids, B vitamins, and antioxidant proteases, all of which play important roles in promoting the growth of K. vulgare. Furthermore, Vitamin C produced by VTC2 could further relieve the oxidative stress in the environment to increase the production of 2-KLG. Therefore, VTC2 would be of great advantage in working with K. vulgare. Thus, the synthetic microbial consortium "VTC2-K. vulgare" was constructed based on transcriptomics analyses, and the accumulation of 2-KLG was increased by 1.49-fold compared with that of mono-cultured K. vulgare, reaching 13.2 ± 0.52 g/L. In addition, the increased production of 2-KLG was accompanied by the up-regulated activities of superoxide dismutase and catalase in the medium and the up-regulated oxidative stress-related genes (sod, cat and gpd) in K. vulgare. The results indicated that the oxidative stress in the synthetic microbial consortium was efficiently reduced. Thus, systems analysis confirmed a favorable symbiotic relationship between microorganisms, providing guidance for further engineering synthetic consortia.

Project description:BACKGROUND2-Keto-L-gulonic acid (2-KGA), the precursor of vitamin C, is currently produced by two-step fermentation. In the second step, L-sorbose is transformed into 2-KGA by the symbiosis system composed of Ketogulonicigenium vulgare and Bacillus megaterium. Due to the different nutrient requirements and the uncertain ratio of the two strains, the symbiosis system significantly limits strain improvement and fermentation optimization.RESULTSIn this study, Ketogulonicigenium robustum SPU_B003 was reported for its capability to grow well independently and to produce more 2-KGA than that of K. vulgare in a mono-culture system. The complete genome of K. robustum SPU_B003 was sequenced, and the metabolic characteristics were analyzed. Compared to the four reported K. vulgare genomes, K. robustum SPU_B003 contained more tRNAs, rRNAs, NAD and NADP biosynthetic genes, as well as regulation- and cell signaling-related genes. Moreover, the amino acid biosynthesis pathways were more complete. Two species-specific internal promoters, P1 (orf_01408 promoter) and P2 (orf_02221 promoter), were predicted and validated by detecting their initiation activity. To efficiently produce 2-KGA with decreased CO2 release, an innovative acetyl-CoA biosynthetic pathway (XFP-PTA pathway) was introduced into K. robustum SPU_B003 by expressing heterologous phosphoketolase (xfp) and phosphotransacetylase (pta) initiated by internal promoters. After gene optimization, the recombinant strain K. robustum/pBBR-P1_xfp2502-P2_pta2145 enhanced acetyl-CoA approximately 2.4-fold and increased 2-KGA production by 22.27% compared to the control strain K. robustum/pBBR1MCS-2. Accordingly, the transcriptional level of the 6-phosphogluconate dehydrogenase (pgd) and pyruvate dehydrogenase genes (pdh) decreased by 24.33?±?6.67 and 8.67?±?5.51%, respectively. The key genes responsible for 2-KGA biosynthesis, sorbose dehydrogenase gene (sdh) and sorbosone dehydrogenase gene (sndh), were up-regulated to different degrees in the recombinant strain.CONCLUSIONSThe genome-based functional analysis of K. robustum SPU_B003 provided a new understanding of the specific metabolic characteristics. The new XFP-PTA pathway was an efficient route to enhance acetyl-CoA levels and to therefore promote 2-KGA production.

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Solid-Liquid Equilibrium in the System 2-Keto-L-Gulonic Acid + L-Ascorbic Acid + Water.

Publications

Solid-Liquid Equilibrium in the System 2-Keto-<i>L</i>-Gulonic Acid + <i>L</i>-Ascorbic Acid + Water.

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