Enhanced succinic acid productivity by expression of mgtCB gene in Escherichia coli mutant

Hydrolysis of lignocellulose to succinic acid: a review of treatment methods and succinic acid applications

Succinic acid (SA) is an intermediate product of the tricarboxylic acid cycle (TCA) and is one of the most significant platform chemicals for the production of various derivatives with high added value. Due to the depletion of fossil raw materials and the demand for eco-friendly energy sources, SA biosynthesis from renewable energy sources is gaining attention for its environmental friendliness. This review comprehensively analyzes strategies for the bioconversion of lignocellulose to SA based on the lignocellulose pretreatment processes and cellulose hydrolysis and fermentation principles and highlights the research progress on acid production and SA utilization under different microbial culture conditions. In addition, the fermentation efficiency of different microbial strains for the production of SA and the main challenges were analyzed. The future application directions of SA derivatives were pointed out. It is expected that this research will provide a reference for the optimization of SA production from lignocellulose.

Residual biomass from surfactin production is a source of arginase and adsorbed surfactin that is useful for environmental remediation

Lipopeptides are important secondary metabolites produced by microbes. They find applications in environmental decontamination and in the chemical, pharmaceutical and food industries. However, their production is expensive. In the present work we propose three strategies to lower the production costs of surfactin. First, the coproduction of surfactin and arginase in a single growth. Second, extract the fraction of surfactin that adsorbs to the biomass and is removed from the growth medium through centrifugation. Third, use microbial biomass for the remediation of organic and inorganic contaminants. The coproduction of surfactin and arginase was evaluated by factorial design experiments using the LB medium supplemented with arginine. The best conditions for surfactin production were 22 h of growth at 37 °C using LB supplemented with arginine 7.3 g/L. Almost similar conditions were found to produce highest levels of arginase, 24 h and 6.45 g/L arginine. Decontamination of phenol and copper from artificial samples was attained by treatment with residues from lipopeptide production. Thus, cell suspensions and wash-waters used to extract surfactin from the biomass. Cell suspensions were used to successfully remove hydroquinone. Cell suspensions and wash-waters containing surfactin were successfully used to recover copper from solution. Specific monitoring methods were used for phenol and metal solutions, respectively a biosensor based on tyrosinase and either atomic absorption flame ionization spectrometry or absorbance coupled to the Arduino™ platform. Therefore, we report three alternative strategies to lower the production costs in lipopeptide production, which include the effective recovery of copper and phenol from contaminated waters using residues from surfactin production. Sustainable and profitable production of surfactin can be achieved by a coproduction strategy of lipopeptides and enzymes. Lipopeptides are collected in the supernatant and enzymes in the biomass. In addition, lipopeptides that coprecipitate with biomass can be recovered by washing. Lipopeptide wash-waters find applications in remediation and cells can also be used for environmental decontamination.

The Impact of SlyA on Cell Metabolism of Salmonella typhimurium: A Joint Study of Transcriptomics and Metabolomics

SlyA is an important transcriptional regulator in Salmonella typhimurium (S. typhimurium). Numerous reports have indicated the impact of SlyA on the virulence of S. typhimurium. Less information regarding the role of SlyA in the cell metabolism of S. typhimurium is available. To close this gap, we compared the growth kinetics of an S. typhimurium wild-type strain to a slyA deletion mutant strain. The data suggested that the cell growth of S. typhimurium was impaired when slyA abolished, indicating that SlyA might affect the cell metabolism of S. typhimurium. To determine the role of SlyA in cell metabolism, we analyzed the metabolite profiles of S. typhimurium in the presence or absence of slyA using gas chromatography coupled with tandem mass spectrometry (GC-MS-MS). With the aim of appropriately interpreting the results obtained from metabolomics, a transcriptomic analysis on both the wild-type S. typhimurium and the slyA deletion mutant was performed. The metabolome data indicated that several glycolysis and lipid metabolism-associated pathways, including the turnover of glycerolipid, pyruvate, butanoate, and glycerophospholipid, were affected in the absence of slyA. In addition, the mRNA levels of several genes associated with glycolysis and lipid turnover were downregulated when slyA was deleted, including pagP, fadL, mgtB, iacp, and yciA. Collectively, these evidence suggested that SlyA affects the glycolysis and lipid turnover of S. typhimurium at a transcriptional level. The raw data of metabolomics is available in the MetaboLights database with an access number of MTBLS1858. The raw data of transcriptome is available in the Sequence Read Archive (SRA) database with an access number of PRJNA656165.

Primary metabolites from overproducing microbial system using sustainable substrates

Primary (or secondary) metabolites are produced by animals, plants, or microbial cell systems either intracellularly or extracellularly. Production capabilities of microbial cell systems for many types of primary metabolites have been exploited at a commercial scale. But the high production cost of metabolites is a big challenge for most of the bioprocess industries and commercial production needs to be achieved. This issue can be solved to some extent by screening and developing the engineered microbial systems via reconstruction of the genome-scale metabolic model. The predicted genetic modification is applied for an increased flux in biosynthesis pathways toward the desired product. Wherein the resulting microbial strain is capable of converting a large amount of carbon substrate to the expected product with minimum by-product formation in the optimal operating conditions. Metabolic engineering efforts have also resulted in significant improvement of metabolite yields, depending on the nature of the products, microbial cell factory modification, and the types of substrate used. The objective of this review is to comprehend the state of art for the production of various primary metabolites by microbial strains system, focusing on the selection of efficient strain and genetic or pathway modifications, applied during strain engineering.

Efficient production of succinic acid in engineered Escherichia coli strains controlled by anaerobically-induced nirB promoter using sweet potato waste hydrolysate

Succinic acid has attracted interest worldwide as a precursor of many industrially crucial chemicals. Biosynthesis of succinic acid from biomass is developing as an environmentally friendly strategy now. Conversion of sweet potato waste (SPW) to succinic acid could implement high-value utilization of biomass, cut cost of the fermentation process and reduce the pollution of environment. Engineered Escherichia coli (E. coli) strain HD134 under the control of anaerobically-induced nirB promoter from Salmonella enterica (P_SnirB) could produce about 16.30 g/L succinic acid with a yield of 0.83 g/g after 48 h on glucose. With SPW hydrolysate as the substrate, 18.65 g/L succinic acid with a yield of 0.94 g/g after 48 h fermentation achieved. Compared to SD134 under Trc control induced with Isopropyl β-D-Thiogalactoside (IPTG), this concentration and yield represented an 8.56% and 6.82% increase, respectively. The use of anaerobically-induced P_SnirB not only could attain higher production of succinic acid than IPTG-induced Trc promoter, but omit cost of expensive exogenous inducers. The efficient production of succinic acid from SPW was firstly studied by anaerobically-induced P_SnirB control, which achieved relative lower cost compared to glucose as substrate and IPTG as the inducer. This novel fermentation process conduces to the cosmically industrial succinic acid bioproduction.

High-level, constitutive expression of the mgtC gene confers increased thermotolerance on Salmonella enterica serovar Typhimurium

We found that mutations that increased the transcription of the mgtCBR (Mg²⁺ transport-related) operon conferred increased thermotolerance on this organism. The 5' leader of the mgtCBR mRNA contains two short open reading frames (ORFs), mgtM and mgtP, whose translation regulates the expression of the mgtCBR operon by a mechanism that is similar to attenuation in amino acid biosynthetic operons. We obtained two types of mutations that resulted in elevated transcription of the operon: defects in the mgtM ribosome-binding site, impairing the translation of this ORF and deletions encompassing the stop codon of mgtM that extend the translation of this ORF across a downstream Rho termination site. These mgtM mutations give further insights into the mechanism of the transcriptional control of the mgtCBR operon that we discuss in this work. We show that the increased thermotolerance requires elevated expression of the mgtC gene, but functional mgtB and mgtR, which respectively encode an Mg²⁺ transporter and a regulatory protein, are dispensable for this response. MgtC has been shown to have complex functions, including a requirement for virulence, flagella-independent motility and synthesis of cellulose and we now found that it has a role in the regulation of thermotolerance.

A novel riboregulator switch system of gene expression for enhanced microbial production of succinic acid

In this paper, a novel riboregulator Switch System of Gene Expression including an OFF-TO-ON switch and an ON-TO-OFF switch was designed to regulate the expression state of target genes between "ON" and "OFF" by switching the identifiability of ribosome recognition site (RBS) based on the thermodynamic stability of different RNA-RNA hybridizations between RBS and small noncoding RNAs. The proposed riboregulator switch system was employed for the fermentative production of succinic acid using an engineered strain of E. coli JW1021, during which the expression of mgtC gene was controlled at "ON" state and that of pepc and ecaA genes were controlled at the "OFF" state in the lag phase and switched to the "OFF" and "ON" state once the strain enters the logarithmic phase. The results showed that using the strain of JW1021, the yield and productivity of succinic acid can reach 0.91 g g^-1 and 3.25 g L^-1 h^-1, respectively, much higher than those using the strains without harboring the riboregulator switch system.

A real-time control system of gene expression using ligand-bound nucleic acid aptamer for metabolic engineering

Artificial control of bio-functions through regulating gene expression is one of the most important and attractive technologies to build novel living systems that are useful in the areas of chemical synthesis, nanotechnology, pharmacology, cell biology. Here, we present a novel real-time control system of gene regulation that includes an enhancement element by introducing duplex DNA aptamers upstream promoter and a repression element by introducing a RNA aptamer upstream ribosome binding site. With the presence of ligands corresponding to the DNA aptamers, the expression of the target gene can be potentially enhanced at the transcriptional level by strengthening the recognition capability of RNAP to the recognition region and speeding up the separation efficiency of the unwinding region due to the induced DNA bubble around the thrombin-bound aptamers; while with the presence of RNA aptamer ligand, the gene expression can be repressed at the translational level by weakening the recognition capability of ribosome to RBS due to the shielding of RBS by the formed aptamer-ligand complex upstream RBS. The effectiveness and potential utility of the developed gene regulation system were demonstrated by regulating the expression of ecaA gene in the cell-free systems. The realistic metabolic engineering application of the system has also tested by regulating the expression of mgtC gene and thrombin cDNA in Escherichia coli JD1021 for controlling metabolic flux and improving thrombin production, verifying that the real-time control system of gene regulation is able to realize the dynamic regulation of gene expression with potential applications in bacterial physiology studies and metabolic engineering.

A DNA Bubble-Mediated Gene Regulation System Based on Thrombin-Bound DNA Aptamers

We describe here a novel approach to enhance the transcription of a target gene in cell-free systems by symmetrically introducing duplex aptamers upstream to a T7 promoter in both the sense and antisense strands of double-stranded plasmids, which leads to the formation of a DNA bubble due to the none-complementary state of the ssDNA region harboring the aptamer sequences. With the presence of thrombins, the DNA bubble would be enlarged due to the binding of aptamers with thrombins. Consequently, the recognition region of the promoter contained in the DNA bubble can be more easily recognized and bound by RNA polymerases, and the separation efficiency of the unwinding region can also be significantly improved, leading to the enhanced expression of the target gene at the transcriptional level. The effectiveness of the proposed gene regulation system was demonstrated by enhancing the expression of gfp and ecaA genes in cell-free systems.