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L-serine is widely used in the food, cosmetic, and pharmaceutical industries. However, the complicated metabolic network and regulatory mechanism of L-serine production lead to the suboptimal productivity of the direct fermentation of L-serine and limits its large-scale industrial production. In this study, a high-yield L-serine production Escherichia coli strain was constructed by a series of defined genetic modification methodologies. First, L-serine-mediated feedback inhibition was removed and L-serine biosynthetic pathway genes (serAfr, serC, and serB) associated with phosphoglycerate kinase (pgk) were overexpressed. Second, the L-serine conversion pathway was further examined by introducing a glyA mutation (K229G) and deleting other degrading enzymes based on the deletion of initial sdaA. Finally, the L-serine transport system was rationally engineered to reduce uptake and accelerate L-serine export. The optimally engineered strain produced 35 g/L L-serine with a productivity of 0.98 g/L/h and a yield of 0.42 g/g glucose in a 5-L fermenter, the highest productivity and yield of L-serine from glucose reported to date. Furthermore, transcriptome and intermediate metabolite of the high-yield L-serine production Escherichia coli strain were analyzed. The results demonstrated the regulatory mechanism of L-serine production is delicate, and that combined metabolic and bioprocess engineering strategies for L-serine producing strains can improve the productivity and yield. [ABSTRACT FROM AUTHOR]

L-serine is an industrially valuable amino acid that is widely used in the food, cosmetics and pharmaceutical industries. In this study, transcriptome sequencing technology was applied to analyze the changes in gene expression levels during the synthesis of L-serine in Escherichia coli fermentation. The optimal carbon–nitrogen ratio for L-serine synthesis in E. coli was determined by setting five carbon–nitrogen ratios for shake flask fermentation. Transcriptome sequencing was performed on E. coli fermented in five carbon–nitrogen ratio medium in which a total of 791 differentially expressed genes (DEGs) were identified in the CZ4_vs_CZ1 group, including 212 upregulated genes and 579 downregulated genes. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of these DEGs showed that the effect of an altered carbon–nitrogen ratio on the fermentability of E. coli was mainly focused on metabolic pathways such as GABAergic synapse and the two-component system (TCS) in which the genes playing key roles were mainly gadB, gadA, glsA, glnA, narH and narJ. In summary, these potential key metabolic pathways and key genes were proposed to provide valuable information for improving glucose conversion during E. coli fermentation. [ABSTRACT FROM AUTHOR]

Background: Microbial de novo production of l-serine, which is widely used in a range of cosmetic and pharmaceutical products, has attracted increasing attention due to its environmentally friendly characteristics. Previous pioneering work mainly focused on l-serine anabolism; however, in this study, it was found that l-serine could be reimported through the l-serine uptake system, thus hampering l-serine production. Result: To address this challenge, engineering via deletion of four genes, namely, sdaC, cycA, sstT and tdcC, which have been reported to be involved in l-serine uptake in Escherichia coli, was first carried out in the l-serine producer E. coli ES. Additionally, the effects of these genes on l-serine uptake activity and l-serine production were investigated. The data revealed an abnormal phenomenon regarding serine uptake activity. The serine uptake activity of the ΔsdaC mutant was 0.798 nmol min−1 (mg dry weight) −1 after 30 min, decreasing by 23.34% compared to that of the control strain. However, the serine uptake activity of the single sstT, cycA and tdcC mutants increased by 34.29%, 78.29% and 48.03%, respectively, compared to that of the control strain. This finding may be the result of the increased level of sdaC expression in these mutants. In addition, multigene-deletion strains were constructed based on an sdaC knockout mutant. The ΔsdaCΔsstTΔtdcC mutant strain exhibited 0.253 nmol min−1 (mg dry weight) −1l-serine uptake activity and the highest production titer of 445 mg/L in shake flask fermentation, which was more than three-fold the 129 mg/L production observed for the parent. Furthermore, the ΔsdaCΔsstTΔtdcC mutant accumulated 34.8 g/L l-serine with a yield of 32% from glucose in a 5-L fermenter after 36 h. Conclusion: The results indicated that reuptake of l-serine impairs its production and that an engineered cell with reduced uptake can address this problem and improve the production of l-serine in E. coli. [ABSTRACT FROM AUTHOR]

Abstract: Uptake of l-tryptophan in Escherichia coli was carried out by three distinct permeases, Mtr, TnaB, and AroP, respectively. In the present study, the three genes of l-tryptophan uptake system were knocked out from an l-tryptophan-producing strain of E. coli, respectively. The knockout mutants all showed lower l-tryptophan uptake activities and higher l-tryptophan production than their parent. Among the three genes, the knockout of mtr was most critical for both l-tryptophan uptake and l-tryptophan production. The uptake activity of l-tryptophan of the mtr mutant was 1.5nmolmin−1 (mg dry weight)−1, which was decreased by 48% when compared to that of the parent; the production of l-tryptophan of the mtr mutant was 14.7g/l, which was increased by 34% when compared to that of the parent. Furthermore, the physiological and fermentation characteristics caused by gene knockouts were also analyzed. [Copyright &y& Elsevier]

A grand challenge of biological chemical production is the competition between synthetic circuits and host genes for limited cellular resources. Quorum sensing (QS)-based dynamic pathway regulations provide a pathway-independent way to rebalance metabolic flux over the course of the fermentation. Most cases, however, these pathway-independent strategies only have capacity for a single QS circuit functional in one cell. Furthermore, current dynamic regulations mainly provide localized control of metabolic flux. Here, with the aid of engineering synthetic orthogonal quorum-related circuits and global mRNA decay, we report a pathway-independent dynamic resource allocation strategy, which allows us to independently controlling two different phenotypic states to globally redistribute cellular resources toward synthetic circuits. The strategy which could pathway-independently and globally self-regulate two desired cell phenotypes including growth and production phenotypes could totally eliminate the need for human supervision of the entire fermentation. A challenge for biological chemical production is the completion between synthetic circuits and host resources. Here the authors the authors use quorum sensing circuits and global mRNA decay to independently control two phenotypic states. [ABSTRACT FROM AUTHOR]

In this study, the performance of Escherichia coli fermentation for L -serine production was improved by fermentation process optimization and transcriptomic analysis. The induction point, induction temperature, dissolved oxygen level and nitrogen source addition in the fed batch fermentation were studied separately to determine the optimal fermentation process. And transcriptome sequencing was applied to the fermentation process to reveal the key metabolic pathways affecting L -serine production. The results showed that the highest titer of L -serine reached 45.66 g/L with a yield of 0.39 g/g when the induction point, induction temperature, dissolved oxygen level and nitrogen source addition were OD 600 = 15, 39 ℃, 40% and 10%, respectively. Transcriptome sequencing results showed that cysteine and methionine metabolism were closely related to L -serine synthesis, and the addition of L -cysteine to the medium promoted cell growth and sustained accumulation of L -serine. • The fermentation process of L -serine production by Escherichia coli was optimized. • The titer of L -serine by E.coli fermentation increased to 45.66 g/L. • L -cysteine is beneficial to E.coli fermentation. [ABSTRACT FROM AUTHOR]

In the present study, the ability of Escherichia coli to produce L -serine by fermentation using glycerol and glucose was investigated. The results showed that the maximum accumulation of L -serine in glycerol and glucose medium was 634.37 mg/L and 459.27 mg/L, respectively. Transcriptome sequencing was then applied to explore the reasons for this difference, and showed: (1) A total of 2041 differentially expressed genes (DEGs) were screened, and these DEGs were mainly concentrated in biosynthesis of amino acids and histidine metabolism；(2) In the biosynthesis of amino acids, the key genes (e.g., tdcG 、 ilvA and tdcB) involved in the degradation of L -serine to pyruvate were significantly down-regulated; (3) The key genes (e.g., ilvB 、 ilvN and ilvM etc) involved in the degradation of pyruvate to branched-chain amino acids were significantly down-regulated; (4) Many up-regulated genes appeared in the glycine anabolic pathway, which may provide a large number of one-carbon units for the growth of E. coli.; and (5) Transcription levels of regulatory genes in histidine metabolism were down-regulated, which may reduce energy consumption. In summary, the present study provides insight at the genetic level into the construction of high-yielding strains for the efficient use of glycerol for L -serine synthesis. • The fermentation difference of glycerol and glucose was compared. • Transcriptome analysis revealed key metabolic pathways for L -serine production. • Biosynthesis of amino acids and histidine metabolism were key metabolic pathways. • key genes were potential factors affecting L -serine production. [ABSTRACT FROM AUTHOR]