Production of l-methionine by submerged fermentation: A review

Available Strategies for Improving the Biosynthesis of Methionine: A Review

Methionine is the only nonpolar α-amino acid containing sulfur among the eight essential amino acids and is closely related to the metabolism of sulfur-containing compounds in the human body. Widely used in feed, medicine, food, and other fields, the market demand is increasing annually. However, low productivity and high cost largely limit the industrial production of methionine, and many novel production methods still have their own disadvantages. In this paper, the available methods for synthesizing methionine are reviewed and discussed. The latest strategies for improving methionine production are further introduced, including culture medium optimization, mutation technology, expression of key genes in the metabolic pathway, knockout and recombination, as well as the engineering of membrane transporters, the fermentation-enzymatic coupling route, and innovation of CO2 biotransformation.

Peptides Used for Heavy Metal Remediation: A Promising Approach

In recent years, heavy metal pollution has become increasingly prominent, severely damaging ecosystems and biodiversity, and posing a serious threat to human health. However, the results of current methods for heavy metal restoration are not satisfactory, so it is urgent to find a new and effective method. Peptides are the units that make up proteins, with small molecular weights and strong biological activities. They can effectively repair proteins by forming complexes, reducing heavy metal ions, activating the plant's antioxidant defense system, and promoting the growth and metabolism of microorganisms. Peptides show great potential for the remediation of heavy metal contamination due to their special structure and properties. This paper reviews the research progress in recent years on the use of peptides to remediate heavy metal pollution, describes the mechanisms and applications of remediation, and provides references for the remediation of heavy metal pollution.

Thorough research and modification of one-carbon units cycle for improving L-methionine production in Escherichia coli

Methionine is the only one of the essential amino acids that contain sulfur, widely used as a feed additive in agriculture. In this study, the availability of 5-methyl-tetrahydrofolate was confirmed as the main limitation in the complex multibranched biosynthetic pathway of L-methionine. The cycle of one-carbon units was thoroughly investigated and modified to supply 5-methyl-tetrahydrofolate for L-methionine production, such as enhancing the supply of precursor, expediting the conversion rate of the cycle, introducing exogenous serine hydroxymethyltransferase and increasing pool size of one-carbon units carrier. The final strain MYA/pAmFA-4 was able to produce 20.89 g/L L-methionine by fed-batch fermentation, which was the highest titer reported in the literatures. This study is instructive for other metabolites biosynthesized needing one-carbon units or having a complex multibranched biosynthetic pathway.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03625-9.

Construction of exogenous methanol, formate, and betaine modules for methyl donor supply in methionine biosynthesis

Methionine is an essential sulfur-containing amino acid that finds widespread applications in agriculture, medicine, and the food industry. However, the complex and multibranched biosynthetic pathway of methionine has posed significant challenges to its efficient fermentation production. In this study, we employed a modularized synthetic biology strategy to improve the weakest branched pathway of methionine biosynthesis. Three exogenous modules were constructed and assembled to provide methyl donors, which are the primary limiting factors in methionine biosynthesis. The first module utilized added methanol, which was converted into 5,10-methylene-tetrahydrofolate for methionine production but was hindered by the toxicity of methanol. To circumvent this issue, a non-toxic formate module was constructed, resulting in a visible improvement in the methionine titer. Finally, an exogenous betaine module was constructed, which could directly deliver methyl to methionine. The final strain produced 2.87 g/L of methionine in a flask, representing a 20% increase over the starting strain. This study presents a novel strategy for improving and balancing other metabolites that are synthesized through complex multibranched pathways.

Role of Zirconia in Oxide-Zeolite Composite for Thiolation of Methanol with Hydrogen Sulfide to Methanethiol

In this paper, the molecular sieve NaZSM-5 was modified with zirconium dioxide (ZrO₂) by a hydrothermal coating process and other methods. By comparing the effects of the crystal phase structure of ZrO₂ and the compositing method on the physicochemical properties and catalytic performance of the obtained composites, the structure–performance relationship of these composite catalysts was revealed. The results indicate that in the hydrothermal system used for the preparation of NaZSM-5, Zr⁴⁺ is more likely to dissolve from m-ZrO₂ than from t-ZrO₂, which can subsequently enter the molecular sieve, causing a greater degree of desiliconization of the framework. The larger specific surface area (360 m²/g) and pore volume (0.52 cm³/g) of the m-ZrO₂/NaZSM-5 composite catalyst increase the exposure of its abundant acidic (0.078 mmol/g) and basic (0.081 mmol/g) active centers compared with other composites. Therefore, this catalyst exhibits a shorter induction period and better catalytic performance. Furthermore, compared with the impregnation method and mechanochemical method, the hydrothermal coating method produces a greater variety of acid–base active centers in the composite catalyst due to the hydrothermal modifying effect.

Cascade enzymatic synthesis of l-homoserine – mathematical modelling as a tool for process optimisation and design

Mathematical modelling enabled cascade reaction optimisation; 100% increase in product concentration and 18% increase in volume productivity compared to previous work.

Beneficial effects of rumen-protected methionine on nitrogen-use efficiency, histological parameters, productivity and reproductive performance of ruminants

Providing essential amounts of balanced nutrients is one of the most vital aspects of livestock production. Among nutrients, protein has an essential role in many physiological functions of animals. Amino acids in needs for both high and medium yielding ruminant animals are not fully covered by microbial degraded feed sources in the rumen of animals, and they must be met by protecting the proteins from being broken down in the rumen; hence, the dietary supplementation of rumen-protected proteins (RPP), including mainly rumen-protected methionine (RPM), became imperative. Many researchers are interested in studying the role of (RPM) in ruminant animals concerning its effect on milk yield, growth performance, digestibility, dry matter intake and nitrogen utilization efficiency. Unfortunately, results obtained from several investigations regarding RPM indicated great fluctuation between its useful and useless effects in ruminant nutrition particularly during early and late lactation period; therefore, this review article may be helpful for ruminant farm owners when they decide to supplement RPM in animal's diet. Conclusively, supplementation of RPM often has a balanced positive influence, without any reported negative impact on milk yield, growth performance and blood parameters especially in early lactating ruminant animals and when used with the low crude protein diet.

Enhanced L-methionine production by genetically engineered Escherichia coli through fermentation optimization

Microbial fermentation for L-methionine (L-Met) production based on natural renewable resources is attractive and challenging. In this work, the effects of medium composition and fermentation conditions were investigated to improve L-Met production by genetically engineered Escherichia coli MET-3. Statistical optimization techniques including Plackett-Burman (PB) design and Box-Behnken design (BBD) were adopted first to optimize the culture medium. Results of PB-designed experiments indicated that the culture medium components including glucose, yeast extract, KH₂PO₄, and MgSO₄.7H₂O had significant effects on L-Met biosynthesis. With their best-predicted concentration established by BBD (glucose 37.43 g/L, yeast extract 0.95 g/L, KH₂PO₄ 1.82 g/L, and MgSO₄.7H₂O 4.51 g/L), L-Met titer was increased to 3.04 g/L from less than 2.0 g/L. For further enhancement of L-Met biosynthesis, the fermentation conditions of batch cultivation carried out in a 5-L fermentor were optimized, and the optimum results were obtained at an agitation rate of 300 rpm, medium pH of 7.0, and induction temperature of 28 °C. Based on the optimization parameters, fed-batch fermentation with the modified medium was conducted. As a result, great improvement of L-Met titer (12.80 g/L) and yield (0.13 mol/mol) were achieved, with an increase of 38.53% and 30.0% compared with those of the basal medium, respectively. Furthermore, higher L-Met productivity of 0.261 g/L/h was obtained, representing 2.13-fold higher in comparison to the original medium. The results may provide a helpful reference for further study on strain improvement and fermentation control.

Metabolic engineering of Escherichia coli for microbial production of L-methionine

L-methionine has attracted a great deal of attention for its nutritional, pharmaceutical, and clinical applications. In this study, Escherichia coli W3110 was engineered via deletion of a negative transcriptional regulator MetJ and over-expression of homoserine O-succinyltransferase MetA together with efflux transporter YjeH, resulting in L-methionine overproduction which is up to 413.16 mg/L. The partial inactivation of the L-methionine import system MetD via disruption of metI made the engineered E. coli ΔmetJ ΔmetI/pTrcA*H more tolerant to high L-ethionine concentration and accumulated L-methionine to a level 43.65% higher than that of E. coli W3110 ΔmetJ/pTrcA*H. Furthermore, deletion of lysA, which blocks the lysine biosynthesis pathway, led to a further 8.5-fold increase in L-methionine titer of E. coli ΔmetJ ΔmetI ΔlysA/pTrcA*H. Finally, addition of Na₂ S₂ O₃ to the media led to an increase of fermentation titer of 11.45%. After optimization, constructed E. coli ΔmetJ ΔmetI ΔlysA/pTrcA*H was able to produce 9.75 g/L L-methionine with productivity of 0.20 g/L/h in a 5 L bioreactor. This novel metabolically tailored strain of E. coli provides an efficient platform for microbial production of L-methionine. Biotechnol. Bioeng. 2017;114: 843-851. © 2016 Wiley Periodicals, Inc.

Effect of L- or DL-methionine Supplementation on Nitrogen Retention, Serum Amino Acid Concentrations and Blood Metabolites Profile in Starter Pigs

The objective of the current study was to evaluate the effect of supplementation of either L-methionine (L-Met) or DL-methionine (DL-Met) to diets of starter pigs on nitrogen (N) balance, metabolism, and serum amino acid profile. Eighteen crossbred (Duroc×Landrace×Yorkshire) barrows weighing 15.45±0.88 kg were randomly allotted to 1 of 3 diets with 6 pigs per treatment. The diets included a basal diet (Met-deficient diet) containing 0.24% standardized ileal digestibility Met with all other essential nutrients meeting the pig’s requirements. The other two diets were produced by supplementing the basal diet with 0.12% DL-Met or L-Met. The experiment lasted for 18 days, consisting of a 13-day adaptation period to the diets followed by a 5-day experimental period. Pigs were fed ad libitum and free access to water throughout the experiment. Results showed that the supplementation of either L-Met or DL-Met improved N retention, and serum methionine concentration, and decreased N excretion compared with basal diet (p<0.01). The N retention of pigs fed diets supplemented with the same inclusion levels of DL-Met or L-Met were not different (p>0.05). In conclusion, on equimolar basis DL-Met and L-Met are equally bioavailable as Met sources for starter pigs.

Metabolic fingerprint of dimethyl sulfone (DMSO2) in microbial-mammalian co-metabolism

There is growing awareness that intestinal microbiota alters the energy harvesting capacity of the host and regulates metabolism. It has been postulated that intestinal microbiota are able to degrade unabsorbed dietary components and transform xenobiotic compounds. The resulting microbial metabolites derived from the gastrointestinal tract can potentially enter the circulation system, which, in turn, affects host metabolism. Yet, the metabolic capacity of intestinal microbiota and its interaction with mammalian metabolism remains largely unexplored. Here, we review a metabolic pathway that integrates the microbial catabolism of methionine with mammalian metabolism of methanethiol (MT), dimethyl sulfide (DMS), and dimethyl sulfoxide (DMSO), which together provide evidence that supports the microbial origin of dimethyl sulfone (DMSO2) in the human metabolome. Understanding the pathway of DMSO2 co-metabolism expends our knowledge of microbial-derived metabolites and motivates future metabolomics-based studies on ascertaining the metabolic consequences of intestinal microbiota on human health, including detoxification processes and sulfur xenobiotic metabolism.

Efficient production of methionine from 2-amino-4-methylthiobutanenitrile by recombinant Escherichia coli harboring nitrilase

Methionine as an essential amino acid has been attracting more attention for its important applications in food and feed additives. In this study, for efficient production of methionine from 2-amino-4-methylthiobutanenitrile, a codon-optimized nitrilase gene was newly synthesized and expressed, and the catalytic conditions for methionine production were studied. The optimal temperature and pH for methionine synthesis were 40 °C and 7.5, respectively. The recombinant nitrilase was thermo-stable with half-life of 5.52 h at 40 °C. The substrate loading was optimized in given amount of catalyst and fixed substrate/catalyst ratio mode to achieve higher productivity. Methionine was produced in 100 % conversion within 120 min with a substrate loading of 300 mM. The production of methionine with the immobilized resting cells in packed-bed reactor was investigated. The immobilized nitrilase exhibited good operation stability and retained over 80 % of the initial activity after operating for 100 h. After separation, the purity and the total yield of methionine reached 99.1 and 97 %, respectively. This recombinant nitrilase could be a potential candidate for application in production of methionine.

Metabolic pathways and fermentative production of L-aspartate family amino acids

The L-aspartate family amino acids (AFAAs), L-threonine, L-lysine, L-methionine and L-isoleucine have recently been of much interest due to their wide spectrum of applications including food additives, components of cosmetics and therapeutic agents, and animal feed additives. Among them, L-threonine, L-lysine and L-methionine are three major amino acids produced currently throughout the world. Recent advances in systems metabolic engineering, which combine various high-throughput omics technologies and computational analysis, are now facilitating development of microbial strains efficiently producing AFAAs. Thus, a thorough understanding of the metabolic and regulatory mechanisms of the biosynthesis of these amino acids is urgently needed for designing system-wide metabolic engineering strategies. Here we review the details of AFAA biosynthetic pathways, regulations involved, and export and transport systems, and provide general strategies for successful metabolic engineering along with relevant examples. Finally, perspectives of systems metabolic engineering for developing AFAA overproducers are suggested with selected exemplary studies.