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Improving the Microbial Production of Amino Acids: From Conventional Approaches to Recent Trends
Guoqing Zhang,Xueni Ren,Xiuhong Liang,Yaqun Wang,Dexin Feng,Yujun Zhang,Mo Xian,Huibin Zou 한국생물공학회 2021 Biotechnology and Bioprocess Engineering Vol.26 No.5
Variable industrial strains have been applied in the fermentation of bulk amino acids. Strain discovery and evolution, process optimization are traditional approaches to improve the yield and efficiency of the bio-production process, hence to compete with chemical or enzymatic process in amino acids production. With the fast development of bioengineering and synthetic biology, the strains can be rationally engineered to achieve better performance and gain the capacity in the fermentation of broader range of amino acids, especially for value-added amino acids. This proposed review aims to summarize traditional and recent strains in the microbial production of amino acids, characterize their metabolic pathways and present potential objectives for rational evolution. In addition, this proposed review prospect the recent opportunities and challenges in the microbial production of value-added amino acids (rare amino acids, non-canonical amino acids, and unnatural amino acids).
In Situ Synthesis and Strengthening of Powder Metallurgy High Speed Steel in Addition of LaB6
Weijun Shen,Linping Yu,Zhi Li,Yuehui He,Qiankun Zhang,Huibin Zhang,Yao Jiang,Nan Lin 대한금속·재료학회 2017 METALS AND MATERIALS International Vol.23 No.6
A novel technology which was characterized by the vacuum solid state sintering was developed for powder metallurgyhigh speed steels production. During sintering, both the WC and Mo2C reacted with Fe and transformed toW and Mo rich M6C carbides which were the common hard phases in high speed steels. Also, a high number of W,Mo and Fe were dissolved in VC, forming the MC carbides. The densification of the material mainly relied on thesolubility effect during the M6C and MC carbides formation. By alloying with a 0.1 wt% of LaB6 to the steel, thebending strength and the fracture toughness were improved from 3290 MPa and 25.6 MPam1/2to 4018 MPa and29.4 MPam1/2, respectively. The TEM analysis demonstrated three types of reaction products by the LaB6 addition:the amorphous phase, the core-shell structure and the La2O3 phase. The impurity elements such as the Mg, Al,Si, S, Ca, and O were absorbed following the LaB6 addition. Moreover, the deoxidization effect caused by the LaB6addition promoted the sintering at a high-temperature period which contributed to the bending strength and fracturetoughness improvement.