Sustainable production of 4-hydroxyisoleucine with minimised carbon loss by simultaneously utilising glucose and xylose in engineered Escherichia coli

Systems metabolic engineering and process optimization for efficient l-tyrosine production from high-purity glucose syrup in Escherichia coli

l-tyrosine (l-tyr) is a valuable aromatic amino acid that can be produced via microbial fermentation, providing a sustainable alternative to costly and polluting chemical synthesis. However, industrial production is limited by poor strain performance and inefficient resource utilization. In this study, a high-performance Escherichia coli strain was engineered to address key fermentation bottlenecks for efficient l-tyr synthesis from high-purity glucose syrup. Initially, a "rapid channel" for l-tyr biosynthesis was established by overexpressing aroGfbr and tyrAfbr genes, introducing the pyridoxal 5'-phosphate synthesis pathway, and strengthening tyrosine efflux. Precursor pools of phosphoenolpyruvate and erythrose-4-phosphate were enriched using modular metabolic engineering and dynamic regulation strategies. Co-metabolism of glucose, maltose, and isomaltose was achieved by integrating Bacillus subtilis-derived membrane permease and maltose-6'-phosphate glucosidase, alongside Bifidobacterium adolescentis-derived oligo-1,6-glucosidase, and by employing a suboptimal glucose supplementation feeding strategy. To overcome oxygen limitation, Vitreoscilla hemoglobin was localized to the periplasm via the twin-arginine translocation pathway. Systematic fermentation optimization further improved strain performance, achieving an l-tyr titer, yield, and productivity of 109.2 g/L, 0.292 g/g, and 2.18 g/L/h, respectively-the highest reported to date. This research demonstrates a promising strategy for enhancing l-tyrosine biosynthesis, providing a scalable approach for industrial production and broader applications in microbial metabolic engineering.

Discovery, Herbicidal Activity and Biosynthesis of a Novel Natural Tetramic Acid from Alternaria Species

The tetramic acid moiety is a pivotal structural unit in numerous natural products. As an analogue of the simplest tetramic acid compound tenuazonic acid (TeA), sec-pentyl-TeA (S-TeA) exhibits double herbicidal activity of TeA. Here, this work identifies S-TeA as a novel natural product synthesized by Alternaria alternata and three other filamentous fungi. Chiral analysis confirm the absolute configuration of natural S-TeA as (5S, 6S). Configuration-bioactivity studies reveal that natural (5S, 6S)-S-TeA is the eutomer and possesses the highest herbicidal activity among all tested diastereomers. Biosynthetic analyses demonstrate that threonine is the precursor to S-TeA, beginning with the production of 2-amino-3-methylhexanoic acid (AMHA) via eight enzymes from the branched-chain amino acid (BCAA) biosynthetic pathway, including threonine deaminase, 2-isopropylmalate synthase (IPMS), 3-isopropylmalate dehydratase (IPMDH), isopropylmalate dehydrogenase (ISMD), acetolactate synthase, ketol-acid reductoisomerase, dihydroxy acid dehydratase, and BCAA aminotransferase. Subsequently, AMHA undergoes acetylation and cyclization by non-ribosomal peptide synthetases to form S-TeA. Distinct differences in the biosynthetic pathways of S-TeA and TeA are identified. In vitro studies confirm the critical roles of three unique enzymes IPMS, IPMDH, and ISMD in S-TeA biosynthesis, which are absent in TeA biosynthesis. These findings provide a solid basis for developing S-TeA as a natural product herbicide.

Oxidative stress in diabetes mellitus and its complications: From pathophysiology to therapeutic strategies

ABSTRACT

Oxidative stress due to aberrant metabolism is considered as a crucial contributor to diabetes and its complications. Hyperglycemia and hyperlipemia boost excessive reactive oxygen species generation by elevated mitochondrial respiration, increased nicotinamide adenine dinucleotide phosphate oxidase activity, and enhanced pro-oxidative processes, including protein kinase C pathways, hexosamine, polyol, and advanced glycation endproducts, which exacerbate oxidative stress. Oxidative stress plays a significant role in the onset of diabetes and its associated complications by impairing insulin production, increasing insulin resistance, maintaining hyperglycemic memory, and inducing systemic inflammation. A more profound comprehension of the molecular processes that link oxidative stress to diabetes is crucial to new preventive and therapeutic strategies. Therefore, this review discusses the mechanisms underlying how oxidative stress contributes to diabetes mellitus and its complications. We also summarize the current approaches for prevention and treatment by targeting the oxidative stress pathways in diabetes.

High-level and -yield orotic acid production in Escherichia coli through systematic modular engineering and "Chaos to Order Cycles" fermentation

Orotic acid is widely used in healthcare and cosmetic industries. However, orotic acid-producing microorganisms are auxotrophic, which results in inefficient microbial production. Herein, a plasmid-free, uninduced, non-auxotrophic orotic acid hyperproducer was constructed from Escherichia coli W3110. Initially, the orotic acid degradation pathway was blocked and the carbamoyl phosphate supply was enriched. Subsequently, pyr operon from Bacillus subtilis F126 was heterologously expressed and precursors' supply was optimized. Thereafter, pyrE was dynamically regulated to reconstruct the non-auxotrophic pathway. Employing fed-batch cultivation, orotic acid titer, yield, and productivity of strain Ora21 reached 182.5 g/L, 0.58 g/g, and 3.80 g/L/h, respectively, the highest levels reported so far. Finally, a novel "Chaos to Order Cycles (COC)" fermentation was developed, which effectively increased the yield to 0.63 g/g. This research is a remarkable achievement in orotic acid production by microbial fermentation and has vast potential for industrial applications.

Growth-coupled production of L-isoleucine in Escherichia coli via metabolic engineering

L-isoleucine, an essential amino acid, is widely used in the pharmaceutical and food industries. However, the current production efficiency is insufficient to meet the increasing demands. In this study, we aimed to develop an efficient L-isoleucine-producing strain of Escherichia coli. First, accumulation of L-isoleucine was achieved by employing feedback-resistant enzymes. Next, a growth-coupled L-isoleucine synthetic pathway was established by introducing the metA-metB-based α-ketobutyrate-generating bypass, which significantly increased L-isoleucine production to 7.4 g/L. Upon employing an activity-improved cystathionine γ-synthase mutant obtained from adaptive laboratory evolution, L-isoleucine production further increased to 8.5 g/L. Subsequently, the redox flux was improved by bypassing the NADPH-dependent aspartate aminotransferase pathway and employing the NADH-dependent pathway and transhydrogenase. Finally, L-isoleucine efflux was enhanced by modifying the transport system. After fed-batch fermentation for 48 h, the resultant strain, ISO-12, reached an L-isoleucine production titer of 51.5 g/L and yield of 0.29 g/g glucose. The strains developed in this study achieved a higher L-isoleucine production efficiency than those reported previously. These strategies will aid in the development of cell factories that produce L-isoleucine and related products.

The Role of Fenugreek in the Management of Type 2 Diabetes

The number of people diagnosed with type 2 diabetes is on the increase worldwide. Of growing concern, the prevalence of type 2 diabetes in children and youths is increasing rapidly and mirrors the increasing burden of childhood obesity. There are many risk factors associated with the condition; some are due to lifestyle, but many are beyond our control, such as genetics. There is an urgent need to develop better therapeutics for the prevention and management of this complex condition since current medications often cause unwanted side effects, and poorly managed diabetes can result in the onset of related comorbidities. Naturally derived compounds have gained momentum for preventing and managing several complex conditions, including type 2 diabetes. Here, we provide an update on the benefits and limitations of fenugreek and its components as a therapeutic for type 2 diabetes, including its bioavailability and interaction with the microbiome.

Metabolic bottlenecks of Pseudomonas taiwanensis VLB120 during growth on d-xylose via the Weimberg pathway

The microbial production of value-added chemicals from renewable feedstocks is an important step towards a sustainable, bio-based economy. Therefore, microbes need to efficiently utilize lignocellulosic biomass and its dominant constituents, such as d-xylose. Pseudomonas taiwanensis VLB120 assimilates d-xylose via the five-step Weimberg pathway. However, the knowledge about the metabolic constraints of the Weimberg pathway, i.e., its regulation, dynamics, and metabolite fluxes, is limited, which hampers the optimization and implementation of this pathway for bioprocesses. We characterized the Weimberg pathway activity of P. taiwanensis VLB120 in terms of biomass growth and the dynamics of pathway intermediates. In batch cultivations, we found excessive accumulation of the intermediates d-xylonolactone and d-xylonate, indicating bottlenecks in d-xylonolactone hydrolysis and d-xylonate uptake. Moreover, the intermediate accumulation was highly dependent on the concentration of d-xylose and the extracellular pH. To encounter the apparent bottlenecks, we identified and overexpressed two genes coding for putative endogenous xylonolactonases PVLB_05820 and PVLB_12345. Compared to the control strain, the overexpression of PVLB_12345 resulted in an increased growth rate and biomass generation of up to 30 % and 100 %, respectively. Next, d-xylonate accumulation was decreased by overexpressing two newly identified d-xylonate transporter genes, PVLB_18545 and gntP (PVLB_13665). Finally, we combined xylonolactonase overexpression with enhanced uptake of d-xylonate by knocking out the gntP repressor gene gntR (PVLB_13655) and increased the growth rate and biomass yield by 50 % and 24 % in stirred-tank bioreactors, respectively. Our study contributes to the fundamental knowledge of the Weimberg pathway in pseudomonads and demonstrates how to encounter the metabolic bottlenecks of the Weimberg pathway to advance strain developments and cell factory design for bioprocesses on renewable feedstocks.

Optimization of trans-4-hydroxyproline synthesis pathway by rearrangement center carbon metabolism in Escherichia coli

BACKGROUND

trans-4-Hydroxyproline (T-4-HYP) is a promising intermediate in the synthesis of antibiotic drugs. However, its industrial production remains challenging due to the low production efficiency of T-4-HYP. This study focused on designing the key nodes of anabolic pathway to enhance carbon flux and minimize carbon loss, thereby maximizing the production potential of microbial cell factories.

RESULTS

First, a basic strain, HYP-1, was developed by releasing feedback inhibitors and expressing heterologous genes for the production of trans-4-hydroxyproline. Subsequently, the biosynthetic pathway was strengthened while branching pathways were disrupted, resulting in increased metabolic flow of α-ketoglutarate in the Tricarboxylic acid cycle. The introduction of the NOG (non-oxidative glycolysis) pathway rearranged the central carbon metabolism, redirecting glucose towards acetyl-CoA. Furthermore, the supply of NADPH was enhanced to improve the acid production capacity of the strain. Finally, the fermentation process of T-4-HYP was optimized using a continuous feeding method. The rate of sugar supplementation controlled the dissolved oxygen concentrations during fermentation, and Fe2+ was continuously fed to supplement the reduced iron for hydroxylation. These modifications ensured an effective supply of proline hydroxylase cofactors (O2 and Fe2+), enabling efficient production of T-4-HYP in the microbial cell factory system. The strain HYP-10 produced 89.4 g/L of T-4-HYP in a 5 L fermenter, with a total yield of 0.34 g/g, the highest values reported by microbial fermentation, the yield increased by 63.1% compared with the highest existing reported yield.

CONCLUSION

This study presents a strategy for establishing a microbial cell factory capable of producing T-4-HYP at high levels, making it suitable for large-scale industrial production. Additionally, this study provides valuable insights into regulating synthesis of other compounds with α-ketoglutaric acid as precursor.

Exploring L-isoleucine riboswitches for enhancing 4-hydroxyisoleucine production in Corynebacterium glutamicum

OBJECTIVES

To explore an L-isoleucine (Ile)-induced biosensor for down-regulation of Ile synthesis pathway and enhancement of 4-hydroxyisoleucine (4-HIL) production in Corynebacterium glutamicum SN01.

RESULTS

Four Ile-induced riboswitches (IleRSN) with different strength were screened from mutation library based on TPP riboswitch. Firstly, IleRSN were integrated into the chromosome of strain SN01 immediately upstream of ilvA gene. The 4-HIL titer of strains carrying PtacM-driven IleRS1 or IleRS3 (14.09 ± 1.07, 15.20 ± 0.93 g 4-HIL L-1) were similar with control strain S-D5I (15.73 ± 2.66 g 4-HIL L-1). Then, another copy of IleRS3-ilvA was integrated downstream of the chromosomal cg0963 gene in SN01-derived strain D-RS with down-regulated L-lysine (Lys) biosynthesis. The Ile supply and 4-HIL titer increased in ilvA two-copy strains KIRSA-3-D5I and KIRSA-3-9I, and Ile concentration was maintained less than 35 mmol L-1 under the control of IleRS3 during fermentation. The resulting strain KIRSA-3-9I produced 22.46 ± 0.96 g 4-HIL L-1.

CONCLUSION

The screened IleRS was effective in the dynamic down-regulation of Ile synthesis pathway in C. glutamicum, and IleRSN with different strength can be applied in various conditions.

High-level and -yield production of L-leucine in engineered Escherichia coli by multistep metabolic engineering

L-leucine is an essential amino acid widely used in food and pharmaceutical industries. However, the relatively low production efficiency limits its large-scale application. In this study, we rationally developed an efficient L-leucine-producing Escherichia coli strain. Initially, the L-leucine synthesis pathway was enhanced by overexpressing feedback-resistant 2-isopropylmalate synthase and acetohydroxy acid synthase both derived from Corynebacterium glutamicum, along with two other native enzymes. Next, the pyruvate and acetyl-CoA pools were enriched by deleting competitive pathways, employing the nonoxidative glycolysis pathway, and dynamically modulating the citrate synthase activity, which significantly promoted the L-leucine production and yield to 40.69 g/L and 0.30 g/g glucose, respectively. Then, the redox flux was improved by substituting the native NADPH-dependent acetohydroxy acid isomeroreductase, branched chain amino acid transaminase, and glutamate dehydrogenase with their NADH-dependent equivalents. Finally, L-leucine efflux was accelerated by precise overexpression of the exporter and deletion of the transporter. Under fed-batch conditions, the final strain LXH-21 produced 63.29 g/L of L-leucine, with a yield and productivity of 0.37 g/g glucose and 2.64 g/(L h), respectively. To our knowledge, this study achieved the highest production efficiency of L-leucine to date. The strategies presented here will be useful for engineering E. coli strains for producing L-leucine and related products on an industrial scale.