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  • MDPI AG  (3)
  • 1
    Online Resource
    Online Resource
    Model Test Study on Natural Thawing Temperature Field of Artificial Ground Frozen Wall
    MDPI AG ; 2023
    In:  Sustainability Vol. 15, No. 4 ( 2023-02-09), p. 3186-
    Details
    In: Sustainability, MDPI AG, Vol. 15, No. 4 ( 2023-02-09), p. 3186-
    Abstract: In order to visualize the evolution and distribution law of the ground temperature field during artificial freezing construction, an indoor model test study was carried out based on the independently constructed hygrothermal coupling artificial ground freezing test platform. The test results show that the soil temperature in the freezing process went through the three stages of a steep drop, a slow drop, and stabilization, the earliest closure position of the frozen wall was the intermediate point between two freezing pipes, and the thickness of the frozen wall on different sections showed Section 1 〉 Section 2 〉 Section 3 after 61 min of positive freezing. The soil temperature in the natural thawing process went through the four stages of a rapid rise, short hysteresis, a second rapid rise, and a linear slow rise. By fitting the test data, the distribution function of the pipe wall temperature along the pipe length under natural thawing conditions was obtained. The research results can provide a valid basis for the numerical calculation model of a three-dimensional non-uniform natural thawing temperature field and can also provide a reference for the design of settlement grouting under natural thawing conditions.
    Type of Medium: Online Resource
    ISSN: 2071-1050
    URL: Article
    DOI: 10.3390/su15043186
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2518383-7
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  • 2
    Online Resource
    Online Resource
    Production of d-Tagatose by Whole-Cell Conversion of Recombinant Bacillus subtilis in the Absence of Antibiotics
    MDPI AG ; 2021
    In:  Biology Vol. 10, No. 12 ( 2021-12-16), p. 1343-
    Details
    In: Biology, MDPI AG, Vol. 10, No. 12 ( 2021-12-16), p. 1343-
    Abstract: d-tagatose is a popular functional monosaccharide produced from lactose by β-galactosidase and arabinose isomerase. In this study, two d-alanine-deficient heterologous gene expression systems were constructed, B. subtilis 168 D1 and B. subtilis 168 D2, using overlapping extension PCR and the CRE/loxP system. The lacZ gene for β-galactosidase was integrated into a specific locus of the chassis B. subtilis 168 D2. A mutually complementary plasmid pMA5 with the alanine racemase gene alrA attached to it was constructed and used to assemble recombinant plasmids overexpressing β-galactosidase and arabinose isomerase. Afterward, an integrated recombinant was constructed by the plasmid expressing the arabinose isomerase gene araA of E. coli transform-competent B. subtilis 168 D2 cells. The co-expressing plasmids were introduced into alanine racemase knockout B. subtilis 168 D1. Whole-cell bioconversion was performed using the integrated recombinant with a maximum yield of 96.8 g/L d-tagatose from 500 g/L lactose, and the highest molar conversions were 57.2%. B. subtilis 168 D1/pMA5-alrA-araA-lacZ is capable of single-cell one-step production of d-tagatose. This study provides a new approach to the production of functional sugars.
    Type of Medium: Online Resource
    ISSN: 2079-7737
    URL: Article
    DOI: 10.3390/biology10121343
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
    detail.hit.zdb_id: 2661517-4
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  • 3
    Online Resource
    Online Resource
    Heterologous Expression of Thermotolerant α-Glucosidase in Bacillus subtilis 168 and Improving Its Thermal Stability by Constructing Cyclized Proteins
    MDPI AG ; 2022
    In:  Fermentation Vol. 8, No. 10 ( 2022-09-29), p. 498-
    Details
    In: Fermentation, MDPI AG, Vol. 8, No. 10 ( 2022-09-29), p. 498-
    Abstract: α-glucosidase is an essential enzyme for the production of isomaltooligosaccharides (IMOs). Allowing α-glucosidase to operate at higher temperatures (above 60 °C) has many advantages, including reducing the viscosity of the reaction solution, enhancing the catalytic reaction rate, and achieving continuous production of IMOs. In the present study, the thermal stability of α-glucosidase was significantly improved by constructing cyclized proteins. We screened a thermotolerant α-glucosidase (AGL) with high transglycosylation activity from Thermoanaerobacter ethanolicus JW200 and heterologously expressed it in Bacillus subtilis 168. After forming the cyclized α-glucosidase by different isopeptide bonds (SpyTag/SpyCatcher, SnoopTag/SnoopCatcher, SdyTag/SdyCatcher, RIAD/RIDD), we determined the enzymatic properties of cyclized AGL. The optimal temperature of all cyclized AGL was increased by 5 °C, and their thermal stability was generally improved, with SpyTag-AGL-SpyCatcher having a 1.74-fold increase compared to the wild-type. The results of molecular dynamics simulations showed that the RMSF values of cyclized AGL decreased, indicating that the rigidity of the cyclized protein increased. This study provides an efficient method for improving the thermal stability of α-glucosidase.
    Type of Medium: Online Resource
    ISSN: 2311-5637
    URL: Article
    DOI: 10.3390/fermentation8100498
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2813985-9
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