[Objective] The aim was to construct threonine-producing strain M122 overexpressing key gene rhtB for transporter protein to transport threonine to the extracellular, and to investigate effects of different carbon or ...[Objective] The aim was to construct threonine-producing strain M122 overexpressing key gene rhtB for transporter protein to transport threonine to the extracellular, and to investigate effects of different carbon or nitrogen sources and pH values on L-threonine production caused by the recombinant strain. [Method] The fermentation process of L-threonine-producing strain was analyzed by different carbon or nitrogen sources, and carbon or nitrogen sources and pH in fermentation medium were also optimized in this study. [Result] After direct modification, the uti- lization efficiency of threonine-producing strain on nutrients increases. When sucrose was used as carbon source for fermentation, Lothreonine yield via shaking culture was 28.1 g/L When （NH4）2SO4 or yeast powder was used as nitrogen source for fermenta- tion, L-threonine yield was 27.8 and 28.2 g/L respectively, which were all higher than that of other nitrogen sources. The study on optimal pH value showed that it was more beneficial for strain growth and L-threonine yield on neutral condition. [Conclusion] The best carbon source for threonine-produing strain M122 was sucrose, while the best nitrogen source was （NH4）2804 or yeast powder, and the most suit- able pH value was 7.0.展开更多
The diffusion coefficients of aqueous L-threonine solutions were determined from 298.15 K to 328.15 K by the metallic diaphragm cell method with accuracy, promptness and convenience. Meanwhile, the densities and visco...The diffusion coefficients of aqueous L-threonine solutions were determined from 298.15 K to 328.15 K by the metallic diaphragm cell method with accuracy, promptness and convenience. Meanwhile, the densities and viscosities of the solutions were also determined and correlated. Based on a semi-empirical model for correlating the diffusion coefficients of some amino acids in their aqueous solutions, a new semi-empirical model for correlating the diffusion coefficients involving temperature was provided, which is more comprehensive and less experiment dependent compared to the previous model. The fitting results are satisfactory. Compared to a former model for correlating the diffusion coefficients of solid organic salts in their aqueous solutions, this model provides significant improvement in correlation of diffusion coefficients with different temperatures avoiding arduous work.展开更多
Two experiments were conducted to evaluate the growth response and serum concentrations （SC） of amino acids （AA） in pigs fed wheat-based diets with either deficient, adequate or excess Lys and Thr. Previously, the...Two experiments were conducted to evaluate the growth response and serum concentrations （SC） of amino acids （AA） in pigs fed wheat-based diets with either deficient, adequate or excess Lys and Thr. Previously, the standardized ileal digestibilities of AA in a basal diet were determined with five ileal cannulated pigs in a digestion trial. In experiment 1, 21 pigs （12.5±0.91 kg） were used to evaluate the effect of adding 0%, 0.69%, and 1.38% free L-Lys. The best growth response was obtained with 0.69% added L-Lys, equivalent to 1.05% total in the diet. The SC of Arg, Thr, and Val were lower （P 〈 0.05） in pigs fed the Lys adequate diet, compared to the deficient, but no further change occurred with excess Lys （P 〉 0.10）. Lys SC increased with each increment in the dietary Lys content （P 〈 0.05）. In experiment 2, 20 pigs （14.3 ± 1.57 kg） were used, and the addition of 0%, 0.14%, 0.28%, and 0.42% crystalline Thr, to the 0.69% L-Lys-supplemented basal diet, was evaluated. The best response was obtained with added 0.28% L-Thr, （0.66% total Thr）, but excess Thr reduced feed intake and growth rate. Moderate and excess levels of Yhr increased the SC of Thr, but excess reduced those of Va[ and Lys. These data show that excess Thr, but not Lys, affect the performance of growing pigs. Also, these data indicate that Val may become limiting in low protein diets with excess Lys or Thr.展开更多
基金Supported by the Science and Technology Supportive Project(Agriculture)Foundation of Huai'an City,Jiangsu Province of China(SN1049)~~
文摘[Objective] The aim was to construct threonine-producing strain M122 overexpressing key gene rhtB for transporter protein to transport threonine to the extracellular, and to investigate effects of different carbon or nitrogen sources and pH values on L-threonine production caused by the recombinant strain. [Method] The fermentation process of L-threonine-producing strain was analyzed by different carbon or nitrogen sources, and carbon or nitrogen sources and pH in fermentation medium were also optimized in this study. [Result] After direct modification, the uti- lization efficiency of threonine-producing strain on nutrients increases. When sucrose was used as carbon source for fermentation, Lothreonine yield via shaking culture was 28.1 g/L When （NH4）2SO4 or yeast powder was used as nitrogen source for fermenta- tion, L-threonine yield was 27.8 and 28.2 g/L respectively, which were all higher than that of other nitrogen sources. The study on optimal pH value showed that it was more beneficial for strain growth and L-threonine yield on neutral condition. [Conclusion] The best carbon source for threonine-produing strain M122 was sucrose, while the best nitrogen source was （NH4）2804 or yeast powder, and the most suit- able pH value was 7.0.
基金Supported by the Educational Ministry Doctor Foundation of China (No. 2000005608).
文摘The diffusion coefficients of aqueous L-threonine solutions were determined from 298.15 K to 328.15 K by the metallic diaphragm cell method with accuracy, promptness and convenience. Meanwhile, the densities and viscosities of the solutions were also determined and correlated. Based on a semi-empirical model for correlating the diffusion coefficients of some amino acids in their aqueous solutions, a new semi-empirical model for correlating the diffusion coefficients involving temperature was provided, which is more comprehensive and less experiment dependent compared to the previous model. The fitting results are satisfactory. Compared to a former model for correlating the diffusion coefficients of solid organic salts in their aqueous solutions, this model provides significant improvement in correlation of diffusion coefficients with different temperatures avoiding arduous work.
文摘Two experiments were conducted to evaluate the growth response and serum concentrations （SC） of amino acids （AA） in pigs fed wheat-based diets with either deficient, adequate or excess Lys and Thr. Previously, the standardized ileal digestibilities of AA in a basal diet were determined with five ileal cannulated pigs in a digestion trial. In experiment 1, 21 pigs （12.5±0.91 kg） were used to evaluate the effect of adding 0%, 0.69%, and 1.38% free L-Lys. The best growth response was obtained with 0.69% added L-Lys, equivalent to 1.05% total in the diet. The SC of Arg, Thr, and Val were lower （P 〈 0.05） in pigs fed the Lys adequate diet, compared to the deficient, but no further change occurred with excess Lys （P 〉 0.10）. Lys SC increased with each increment in the dietary Lys content （P 〈 0.05）. In experiment 2, 20 pigs （14.3 ± 1.57 kg） were used, and the addition of 0%, 0.14%, 0.28%, and 0.42% crystalline Thr, to the 0.69% L-Lys-supplemented basal diet, was evaluated. The best response was obtained with added 0.28% L-Thr, （0.66% total Thr）, but excess Thr reduced feed intake and growth rate. Moderate and excess levels of Yhr increased the SC of Thr, but excess reduced those of Va[ and Lys. These data show that excess Thr, but not Lys, affect the performance of growing pigs. Also, these data indicate that Val may become limiting in low protein diets with excess Lys or Thr.
