A High-Efficiency Artificial Synthetic Pathway for 5-Aminovalerate Production From Biobased L-Lysine in Escherichia coli

Metabolic Engineering of High L-Lysine-Producing Escherichia coli for de Novo Production of L-Lysine-Derived Compounds

5-Aminovalerate (5-AVA), 5-hydroxyvalerate (5-HV), and 1,5-pentanediol (1,5-PDO) are l-lysine derivatives with extensive applications in the production of materials such as polyesters, polyurethane, plasticizers, inks, and coatings. However, their large-scale production is limited by the lack of efficient synthetic pathways. Here, we aimed to construct multiple synthetic pathways by screening the key enzymes involved in the synthesis of these compounds in Escherichia coli. The engineered pathway utilizing RaiP demonstrated a superior catalytic efficiency. The LER strain that overexpressed only raiP successfully synthesized 9.70 g/L 5-HV and 8.31 g/L 5-AVA, whereas the strain LERGY that overexpressed raiP, gabT, and yahK accumulated 9.72 g/L 5-HV and 7.95 g/L 5-AVA from 20 g/L glucose. The introduction of exogenous transaminases and dehydrogenases enhanced cell growth and fermentation efficiency with respect to 5-HV synthesis, albeit without significantly impacting the yield. Strain LE05, incorporating only two exogenous enzymes, RaiP and CaR, produced 1.87 g/L 1,5-PDO, 3.85 g/L 5-HV, and 4.78 g/L 5-hydroxyglutaraldehyde from 20 g/L glucose after 6 days. The strain LE02G, fortified with transaminase, dehydrogenase, and NADPH regeneration system, accumulated 7.82 g/L 1,5-PDO, whereas the aldp-knock out LE02G2 synthesized 10.98 g/L 1,5-PDO from 50 g/L glucose in fed-batch fermentation after 6 days, yielding 0.22 g/g glucose (0.37 mol/mol). Introducing the NADPH regeneration pathway and deleting the NADPH-consuming pathways increased the 1,5-PDO yield and decreased the precursor concentration. The proposed pathways and engineering strategies presented in this study can prove instrumental in developing biological routes for the practical production of 5-AVA, 5-HV, and 1,5-PDO.

High-efficiency production of 5-hydroxyectoine using metabolically engineered Corynebacterium glutamicum

BACKGROUND

Extremolytes enable microbes to withstand even the most extreme conditions in nature. Due to their unique protective properties, the small organic molecules, more and more, become high-value active ingredients for the cosmetics and the pharmaceutical industries. While ectoine, the industrial extremolyte flagship, has been successfully commercialized before, an economically viable route to its highly interesting derivative 5-hydroxyectoine (hydroxyectoine) is not existing.

RESULTS

Here, we demonstrate high-level hydroxyectoine production, using metabolically engineered strains of C. glutamicum that express a codon-optimized, heterologous ectD gene, encoding for ectoine hydroxylase, to convert supplemented ectoine in the presence of sucrose as growth substrate into the desired derivative. Fourteen out of sixteen codon-optimized ectD variants from phylogenetically diverse bacterial and archaeal donors enabled hydroxyectoine production, showing the strategy to work almost regardless of the origin of the gene. The genes from Pseudomonas stutzeri (PST) and Mycobacterium smegmatis (MSM) worked best and enabled hydroxyectoine production up to 97% yield. Metabolic analyses revealed high enrichment of the ectoines inside the cells, which, inter alia, reduced the synthesis of other compatible solutes, including proline and trehalose. After further optimization, C. glutamicum Ptuf ectD^PST achieved a titre of 74 g L^-1 hydroxyectoine at 70% selectivity within 12 h, using a simple batch process. In a two-step procedure, hydroxyectoine production from ectoine, previously synthesized fermentatively with C. glutamicum ectABC^opt, was successfully achieved without intermediate purification.

CONCLUSIONS

C. glutamicum is a well-known and industrially proven host, allowing the synthesis of commercial products with granted GRAS status, a great benefit for a safe production of hydroxyectoine as active ingredient for cosmetic and pharmaceutical applications. Because ectoine is already available at commercial scale, its use as precursor appears straightforward. In the future, two-step processes might provide hydroxyectoine de novo from sugar.

An artificial pathway for trans-4-hydroxy-L-pipecolic acid production from L-lysine in Escherichia coli

Trans-4-hydroxy-L-pipecolic acid (Trans-4-HyPip) is a hydroxylated product of L-pipecolic acid, and which is widely used in pharmaceutical and chemical industry. Here, a trans-4-HyPip biosynthesis module was designed and constructed in Escherichia coli by overexpressing lysine α-oxidase, Δ1-piperideine-2-carboxylase reductase, glucose dehydrogenase, lysine permease, catalase and L-pipecolic acid trans-4-hydroxylase for expanding the lysine catabolism pathway. 4.89 g/L of trans-4-HyPip was generated in shake flasks from 8 g/L of L-pipecolic acid. By this approach, 14.86 g/L of trans-4-HyPip was produced from lysine after 48 h in a 5-L bioreactor. As far as we know, this is the first multi-enzyme cascade catalytic system for the production of trans-4-HyPip using Escherichia coli from L-lysine. Therefore, it can be considered as a potential candidate for industrial production of trans-4-HyPip in microorganisms.

Systems metabolic engineering of Corynebacterium glutamicum eliminates all by-products for selective and high-yield production of the platform chemical 5-aminovalerate

5-aminovalerate (AVA) is a platform chemical of substantial commercial value to derive nylon-5 and five-carbon derivatives like δ-valerolactam, 1,5-pentanediol, glutarate, and 5-hydroxyvalerate. De-novo bio-production synthesis of AVA using metabolically engineered cell factories is regarded as exemplary route to provide this chemical in a sustainable way. So far, this route is limited by low titers, rates and yields and suffers from high levels of by-products. To overcome these limitations, we developed a novel family of AVA producing C. glutamicum cell factories. Stepwise optimization included (i) improved AVA biosynthesis by expression balancing of the heterologous davAB genes from P. putida, (ii) reduced formation of the by-product glutarate by disruption of the catabolic y-aminobutyrate pathway (iii), increased AVA export, and (iv) reduced AVA re-import via native and heterologous transporters to account for the accumulation of intracellular AVA up to 300 mM. Strain C. glutamicum AVA-5A, obtained after several optimization rounds, produced 48.3 g L^-1 AVA in a fed-batch process and achieved a high yield of 0.21 g g^-1. Surprisingly in later stages, the mutant suddenly accumulated glutarate to an extent equivalent to 30% of the amount of AVA formed, tenfold more than in the early process, displaying a severe drawback toward industrial production. Further exploration led to the discovery that ArgD, naturally aminating N-acetyl-l-ornithine during l-arginine biosynthesis, exhibits deaminating side activity on AVA toward glutarate formation. This promiscuity became relevant because of the high intracellular AVA level and the fact that ArgD became unoccupied with the gradually stronger switch-off of anabolism during production. Glutarate formation was favorably abolished in the advanced strains AVA-6A, AVA-6B, and AVA-7, all lacking argD. In a fed-batch process, C. glutamicum AVA-7 produced 46.5 g L^-1 AVA at a yield of 0.34 g g^-1 and a maximum productivity of 1.52 g L^-1 h^-1, outperforming all previously reported efforts and stetting a milestone toward industrial manufacturing of AVA. Notably, the novel cell factories are fully genome-based, offering high genetic stability and requiring no selection markers.

Parishin From Gastrodia Elata Ameliorates Aging Phenotype in Mice in a Gut Microbiota-Related Manner

The physiological and pathological processes that accompany aging can seriously affect the quality of life of the elderly population. Therefore, delaying aging and developing antiaging products have become popular areas of inquiry. Gut microbiota plays an important role in age-related phenotypes. The present study aimed to investigate the antiaging effects and underlying mechanism of parishin, a phenolic glucoside isolated from traditional Chinese medicine Gastrodia elata. Samples from adult (12 weeks), low-dose (10 mg/kg/d) or high-dose (20 mg/kg/d) parishin-treated and untreated aged (19 months) mice were collected to determine blood indicators, gut microbiota and metabolome, and cardiopulmonary histopathological features. The results showed that parishin treatment ameliorates aging-induced cardiopulmonary fibrosis and increase in serum p16^Ink4a, GDF15, and IL-6 levels. Furthermore, parishin treatment alleviated dysbiosis in gut microbiota, including altered microbial diversity and the aberrant abundance of opportunistic pathogenic bacteria such as Turicibacter and Erysipelatoclostridium. Gene function prediction and gut metabolome analysis results indicated that the parishin treatment-altered gut microbiota played important roles in sugar, lipid, amino acid and nucleic acid metabolism, and improved gut metabolic disorders in aged mice. In conclusion, the present study provides an experimental basis of potential applications of parishin against aging.

An Artificial Pathway for N-Hydroxy-Pipecolic Acid Production From L-Lysine in Escherichia coli

N-hydroxy-pipecolic acid (NHP) is a hydroxylated product of pipecolic acid and an important systemic acquired resistance signal molecule. However, the biosynthesis of NHP does not have a natural metabolic pathway in microorganisms. Here, we designed and constructed a promising artificial pathway in Escherichia coli for the first time to produce NHP from biomass-derived lysine. This biosynthesis route expands the lysine catabolism pathway and employs six enzymes to sequentially convert lysine into NHP. This artificial route involves six functional enzyme coexpression: lysine α-oxidase from Scomber japonicus (RaiP), glucose dehydrogenase from Bacillus subtilis (GDH), Δ1-piperideine-2-carboxylase reductase from Pseudomonas putida (DpkA), lysine permease from E. coli (LysP), flavin-dependent monooxygenase (FMO1), and catalase from E. coli (KatE). Moreover, different FMO1s are used to evaluate the performance of the produce NHP. A titer of 111.06 mg/L of NHP was yielded in shake flasks with minimal medium containing 4 g/L of lysine. By this approach, NHP has so far been produced at final titers reaching 326.42 mg/L by 48 h in a 5-L bioreactor. To the best of our knowledge, this is the first NHP process using E. coli and the first process to directly synthesize NHP by microorganisms. This study lays the foundation for the development and utilization of renewable resources to produce NHP in microorganisms.

Coproduction of 5-Aminovalerate and δ-Valerolactam for the Synthesis of Nylon 5 From L-Lysine in Escherichia coli

The compounds 5-aminovalerate and δ-valerolactam are important building blocks that can be used to synthesize bioplastics. The production of 5-aminovalerate and δ-valerolactam in microorganisms provides an ideal source that reduces the cost. To achieve efficient biobased coproduction of 5-aminovalerate and δ-valerolactam in Escherichia coli, a single biotransformation step from L-lysine was constructed. First, an equilibrium mixture was formed by L-lysine α-oxidase RaiP from Scomber japonicus. In addition, by adjusting the pH and H₂O₂ concentration, the titers of 5-aminovalerate and δ-valerolactam reached 10.24 and 1.82 g/L from 40 g/L L-lysine HCl at pH 5.0 and 10 mM H₂O₂, respectively. With the optimized pH value, the δ-valerolactam titer was improved to 6.88 g/L at pH 9.0 with a molar yield of 0.35 mol/mol lysine. The ratio of 5AVA and δ-valerolactam was obviously affected by pH value. The ratio of 5AVA and δ-valerolactam could be obtained in the range of 5.63:1-0.58:1 at pH 5.0-9.0 from the equilibrium mixture. As a result, the simultaneous synthesis of 5-aminovalerate and δ-valerolactam from L-lysine in Escherichia coli is highly promising. To our knowledge, this result constitutes the highest δ-valerolactam titer reported by biological methods. In summary, a commercially implied bioprocess developed for the coproduction of 5-aminovalerate and δ-valerolactam using engineered Escherichia coli.

Utilization of a Wheat Sidestream for 5-Aminovalerate Production in Corynebacterium glutamicum

Production of plastics from petroleum-based raw materials extensively contributes to global pollution and CO2 emissions. Biotechnological production of functionalized monomers can reduce the environmental impact, in particular when using industrial sidestreams as feedstocks. Corynebacterium glutamicum, which is used in the million-ton-scale amino acid production, has been engineered for sustainable production of polyamide monomers. In this study, wheat sidestream concentrate (WSC) from industrial starch production was utilized for production of l-lysine-derived bifunctional monomers using metabolically engineered C. glutamicum strains. Growth of C. glutamicum on WSC was observed and could be improved by hydrolysis of WSC. By heterologous expression of the genes xylA Xc B Cg (xylA from Xanthomonas campestris) and araBAD Ec from E. coli, xylose, and arabinose in WSC hydrolysate (WSCH), in addition to glucose, could be consumed, and production of l-lysine could be increased. WSCH-based production of cadaverine and 5-aminovalerate (5AVA) was enabled. To this end, the lysine decarboxylase gene ldcC Ec from E. coli was expressed alone or for conversion to 5AVA cascaded either with putrescine transaminase and dehydrogenase genes patDA Ec from E. coli or with putrescine oxidase gene puo Rq from Rhodococcus qingshengii and patD Ec . Deletion of the l-glutamate dehydrogenase-encoding gene gdh reduced formation of l-glutamate as a side product for strains with either of the cascades. Since the former cascade (ldcC Ec -patDA Ec ) yields l-glutamate, 5AVA production is coupled to growth by flux enforcement resulting in the highest 5AVA titer obtained with WSCH-based media.

Evaluation of Heterologous Biosynthetic Pathways for Methanol-Based 5-Aminovalerate Production by Thermophilic Bacillus methanolicus

The use of methanol as carbon source for biotechnological processes has recently attracted great interest due to its relatively low price, high abundance, high purity, and the fact that it is a non-food raw material. In this study, methanol-based production of 5-aminovalerate (5AVA) was established using recombinant Bacillus methanolicus strains. 5AVA is a building block of polyamides and a candidate to become the C5 platform chemical for the production of, among others, δ-valerolactam, 5-hydroxy-valerate, glutarate, and 1,5-pentanediol. In this study, we test five different 5AVA biosynthesis pathways, whereof two directly convert L-lysine to 5AVA and three use cadaverine as an intermediate. The conversion of L-lysine to 5AVA employs lysine 2-monooxygenase (DavB) and 5-aminovaleramidase (DavA), encoded by the well-known Pseudomonas putida cluster davBA, among others, or lysine α-oxidase (RaiP) in the presence of hydrogen peroxide. Cadaverine is converted either to γ-glutamine-cadaverine by glutamine synthetase (SpuI) or to 5-aminopentanal through activity of putrescine oxidase (Puo) or putrescine transaminase (PatA). Our efforts resulted in proof-of-concept 5AVA production from methanol at 50°C, enabled by two pathways out of the five tested with the highest titer of 0.02 g l^-1. To our knowledge, this is the first report of 5AVA production from methanol in methylotrophic bacteria, and the recombinant strains and knowledge generated should represent a valuable basis for further improved 5AVA production from methanol.