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Zhende Zhu,Wenbin Lu,Yanxin He,Xiangcheng Que 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.7
In view of the typical anisotropy of columnar jointed basalt in the dam area of the Baihetan Hydropower Station on the Jinsha River in China, columnar jointed rock mass models with different column angles (α = 0o − 90o) were constructed with similar materials, and three sets of intermittent joints are considered in the physical models. Uniaxial and equal-confining-pressure triaxial compression tests were carried out with a true triaxial testing machine, and the variations of the failure mechanisms, stress-strain relationships, and strength characteristics of the columnar jointed rock masses with the joint inclination angle were investigated under different stress conditions. The results revealed the following: 1) during triaxial compression, two types of stress-strain curves existed, namely the ideal plastic curve and the strain-hardening curve; 2) the strength and elastic modulus of the sample under uniaxial compression presented U-shaped curves with the variation of α. Moreover, the strength of the samples increased with the change of α under triaxial compression, and the elastic modulus Erincreased significantly with the increase of the confining pressure. 3) There were four typical types of failure within the columnar joint samples under triaxial compression. In addition, the test data were used to verify that the Mogi strength criterion good applicability to the columnar jointed rock mass under three-dimensional stress. An empirical prediction model of the relationship between the elastic modulus and confining pressure of the columnar jointed rock mass was established, and its applicable conditions were analyzed. The empirical prediction model is verified by the test results of the columnar jointed rock mass, which indicates that the prediction model was in good agreement with the test data. Finally, the strength characteristics and failure modes of columnar jointed rock masses under different loading conditions were summarized.
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Wei Luo,Jin Huang,Xiangcheng Zhu,Lei Huang,Jin Cai,Zhi-nan Xu 한국식품과학회 2013 Food Science and Biotechnology Vol.22 No.1
The production of L-tryptophan was investigated in a recombinant strain Escherichia coli W3110-ZDrr. It was observed that phosphate and feeding strategies are key factors to ensure the good cell growth and high production of L-tryptophan. The simple exponential feeding strategy could only produce 10.6 g/L L-tryptophan due to the improper feeding rate; while the manual glucose-feedback feeding approach could effectively control the substrate and inhibit the formation of acetate, and thus improvemed the Ltryptophan production to 25.5 g/L. The modified exponential feeding approach avoided overfeeding or underfeeding and achieved high production of L-tryptophan. Moreover, the addition of Tween 60 or PL61 could enhance the cell growth and the production of L-tryptophan in the fed-batch mode. Subsequent metabolic flux analysis showed that more carbon flux was distributed into the biosynthesis of Ltryptophan when Tween 60 or PL61 was supplied. The present work presents one base for further large-scale production of this important amino acid.
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Xueyun Wu,Zhengbin Lv,Yaozhou Zhang,Dong Yang,Xiangcheng Zhu,Zhinan Xu,Zhiyang Feng,Ben Shen 한국생물공학회 2010 Biotechnology and Bioprocess Engineering Vol.15 No.4
The heterologous production of iso-migrastatin (iso-MGS) was successfully demonstrated in an engineered S. lividans SB11002 strain, which was derived from S. lividans K4-114, following introduction of pBS11001,which harbored the entire mgs biosynthetic gene cluster. However, under similar fermentation conditions, the iso-MGS titer in the engineered strain was significantly lower than that in the native producer - Streptomyces platensis NRRL 18993. To circumvent the problem of low iso-MGS titers and to expand the utility of this heterologous system for iso-MGS biosynthesis and engineering, systematic optimization of the fermentation medium was carried out. The effects of major components in the cultivation medium,including carbon, organic and inorganic nitrogen sources,were investigated using a single factor optimization method. As a result, sucrose and yeast extract were determined to be the best carbon and organic nitrogen sources, resulting in optimized iso-MGS production. Conversely, all other inorganic nitrogen sources evaluated produced various levels of inhibition of iso-MGS production. The final optimized R2YE production medium produced iso-MGS with a titer of 86.5 mg/L, about 3.6-fold higher than that in the original R2YE medium, and 1.5 fold higher than that found within the native S. platensis NRRL 18993 producer.
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Discovery of the leinamycin family of natural products by mining actinobacterial genomes
Pan, Guohui,Xu, Zhengren,Guo, Zhikai,Hindra,Ma, Ming,Yang, Dong,Zhou, Hao,Gansemans, Yannick,Zhu, Xiangcheng,Huang, Yong,Zhao, Li-Xing,Jiang, Yi,Cheng, Jinhua,Van Nieuwerburgh, Filip,Suh, Joo-Won,Duan National Academy of Sciences 2017 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.114 No.52
<P>Nature's ability to generate diverse natural products from simple building blocks has inspired combinatorial biosynthesis. The knowledge-based approach to combinatorial biosynthesis has allowed the production of designer analogs by rational metabolic pathway engineering. While successful, structural alterations are limited, with designer analogs often produced in compromised titers. The discovery-based approach to combinatorial biosynthesis complements the knowledge-based approach by exploring the vast combinatorial biosynthesis repertoire found in Nature. Here we showcase the discovery-based approach to combinatorial biosynthesis by targeting the domain of unknown function and cysteine lyase domain (DUF-SH) didomain, specific for sulfur incorporation from the leinamycin (LNM) biosynthetic machinery, to discover the LNM family of natural products. By mining bacterial genomes from public databases and the actinomycetes strain collection at The Scripps Research Institute, we discovered 49 potential producers that could be grouped into 18 distinct clades based on phylogenetic analysis of the DUF-SH didomains. Further analysis of the representative genomes from each of the clades identified 28 lnm-type gene clusters. Structural diversities encoded by the LNM-type biosynthetic machineries were predicted based on bioinformatics and confirmed by in vitro characterization of selected adenylation proteins and isolation and structural elucidation of the guangnanmycins and weishanmycins. These findings demonstrate the power of the discovery-based approach to combinatorial biosynthesis for natural product discovery and structural diversity and highlight Nature's rich biosynthetic repertoire. Comparative analysis of the LNM-type biosynthetic machineries provides outstanding opportunities to dissect Nature's biosynthetic strategies and apply these findings to combinatorial biosynthesis for natural product discovery and structural diversity.</P>
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