Optimization of Fermentation Conditions for the Biosynthesis of l-Threonine by Escherichia coli

Abstract

In this study, the fed-batch fermentation technique was applied to improve the yield of L-threonine produced by Escherichia coli TRFC. Various fermentation substrates and conditions were investigated to identify the optimal carbon source, its concentration and C/N ratio in the production of L-threonine. Sucrose was found to be the optimal initial carbon source and its optimal concentration was determined to be 70 g/L based on the results of fermentations conducted in a 5-L jar fermentor using a series of fed-batch cultures of E. coli TRFC. The effects of glucose concentration and three different feeding methods on the production of L-threonine were also investigated in this work. Our results showed that the production of L-threonine by E. coli was enhanced when glucose concentration varied between 5 and 20 g/L with DO-control pulse fed-batch method. Furthermore, the C/N ratio was a more predominant factor than nitrogen concentration for L-threonine overproduction and the optimal ratio of ammonium sulfate to sucrose (g/g) was 30. Under the optimal conditions, a final L-threonine concentration of 118 g/L was achieved after 38 h with the productivity of 3.1 g/L/h (46% conversion ratio from glucose to threonine).

Tuning of the Carbon-to-Nitrogen Ratio for the Production of l-Arginine by Escherichia coli

“…However, the fact that fermentation was hampered with 30 g/L initial glucose but not with 15 g/L suggests that it is the high concentration of ammonium, or the combination of the high concentrations of ammonium and glucose, rather than the C/N ratio itself, that had such a detrimental effect. A negative impact of excessive ammonium on fermentation has been observed in other studies [15,16,39]. For instance, increasing the initial ammonium sulphate concentration from 10 g/L to 20 g/L resulted in a nearly six-fold decline in L-phenylalanine production and productivity [16].…”

“…However, after a certain threshold, the addition of ammonium sulphate, a common nitrogen source, was detrimental for the production of lysine and succinate by C. glutamicum [13,14] and that of L-threonine and L-phenylalanine by E. coli [15,16]. In addition, an excessive supply of nitrogen might result in large nitrogen wastes, which pose serious environmental threats such as global warming, thinning of the stratospheric ozone layer, and biodiversity loss [17][18][19][20][21].…”

“…The importance of optimizing the C/N ratio in E. coli fermentations has further been demonstrated for heterologous gene expression [30] and for the production of the amino acid L-threonine, where the C/N molar ratio resulting in the best production was 69 [15].…”

Transformation of Biomass into Commodity Chemicals Using Enzymes or Cells

“…391 Higher yields, 0.39 g/g, have been achieved upon metabolic engineering of E. coli. 392 The achievable theoretical yield of L-threonine has been calculated to be 0.81 g/g, if there would be no biomass formation.…”

Effi cient Extraction of Xylan from Delignifi ed Corn Stover Using Dimethyl Sulfi de

“…To resolve the above-mentioned problems, many possible improvements can be achieved to enhance sabinene production. One approach is to optimize the fermentation process by increasing cell density to elevate the yield of products [38,39], using in situ product removal, membrane technology or dissociation of growth or cell mass formation from product formation to reduce the toxicity of sabinene [37]. Another approach is engineering of the host including: employing a chromosome integration technique to decrease the cell growth burden on the host that results from overexpression of heterologous genes [9], expression of efflux pumps, heat shock proteins, membrane modifying proteins, and activation of general stress response genes to improve tolerance of the host to sabinene [2,3,36].…”