The Expression Modulation of the Key Enzyme Acc for Highly Efficient 3-Hydroxypropionic Acid Production

Bioproduction of 3-Hydroxypropionic Acid by Enhancing the Precursor Supply with a Hybrid Pathway and Cofactor Regeneration

3-Hydroxypropionic acid (3-HP) is one of the 12 valuable platform chemicals with versatile applications in the chemical, food, and cosmetic industries. However, the biosynthesis of 3-HP faces challenges due to the lack of robust chassis and the high costs associated with the fermentation process. To address these challenges, we made efforts to augment the robustness of 3-HP-producing chassis by exploiting metabolic regulation, controlling carbon flux, balancing cofactor generation, and optimizing fermentation conditions. First, the malonyl-CoA (MCA) pathway was recruited and rebalanced in Escherichia coli. Subsequently, a hybrid pathway integrating the Embden-Meyerhof-Parnas pathway with the nonoxidative glycolysis pathway was systematically modulated to enhance carbon flux to the MCA pathway, followed by fine-tuning NADPH regeneration. Then, by optimizing the fermentation conditions, 3-HP production was significantly improved, reaching 6.8 g/L. Finally, in a fed-batch experiment, the final chassis produced 42.8 g/L 3-HP, corresponding to a 0.4 mol/mol yield and 0.6 g/(L·h) productivity.

Carbon dioxide valorization into resveratrol via lithoautotrophic fermentation using engineered Cupriavidus necator H16

BACKGROUND

Industrial biomanufacturing of value-added products using CO2 as a carbon source is considered more sustainable, cost-effective and resource-efficient than using common carbohydrate feedstocks. Cupriavidus necator H16 is a representative H2-oxidizing lithoautotrophic bacterium that can be utilized to valorize CO2 into valuable chemicals and has recently gained much attention as a promising platform host for versatile C1-based biomanufacturing. Since this microbial platform is genetically tractable and has a high-flux carbon storage pathway, it has been engineered to produce a variety of valuable compounds from renewable carbon sources. In this study, the bacterium was engineered to produce resveratrol autotrophically using an artificial phenylpropanoid pathway.

RESULTS

The heterologous genes involved in the resveratrol biosynthetic pathway-tyrosine ammonia lyase (TAL), 4-coumaroyl CoA ligase (4CL), and stilbene synthase (STS) -were implemented in C. necator H16. The overexpression of acetyl-CoA carboxylase (ACC), disruption of the PHB synthetic pathway, and an increase in the copy number of STS genes enhanced resveratrol production. In particular, the increased copies of VvSTS derived from Vitis vinifera resulted a 2-fold improvement in resveratrol synthesis from fructose. The final engineered CR-5 strain produced 1.9 mg/L of resveratrol from CO2 and tyrosine via lithoautotrophic fermentation.

CONCLUSIONS

To the best of our knowledge, this study is the first to describe the valorization of CO2 into polyphenolic compounds by engineering a phenylpropanoid pathway using the lithoautotrophic bacterium C. necator H16, demonstrating the potential of this strain a platform for sustainable chemical production.

Increased CO2 fixation enables high carbon-yield production of 3-hydroxypropionic acid in yeast

CO2 fixation plays a key role to make biobased production cost competitive. Here, we use 3-hydroxypropionic acid (3-HP) to showcase how CO2 fixation enables approaching theoretical-yield production. Using genome-scale metabolic models to calculate the production envelope, we demonstrate that the provision of bicarbonate, formed from CO2, restricts previous attempts for high yield production of 3-HP. We thus develop multiple strategies for bicarbonate uptake, including the identification of Sul1 as a potential bicarbonate transporter, domain swapping of malonyl-CoA reductase, identification of Esbp6 as a potential 3-HP exporter, and deletion of Uga1 to prevent 3-HP degradation. The combined rational engineering increases 3-HP production from 0.14 g/L to 11.25 g/L in shake flask using 20 g/L glucose, approaching the maximum theoretical yield with concurrent biomass formation. The engineered yeast forms the basis for commercialization of bio-acrylic acid, while our CO2 fixation strategies pave the way for CO2 being used as the sole carbon source.

Production of 3-Hydroxypropionic Acid from Renewable Substrates by Metabolically Engineered Microorganisms: A Review

3-Hydroxypropionic acid (3-HP) is a platform chemical with a wide range of existing and potential applications, including the production of poly(3-hydroxypropionate) (P-3HP), a biodegradable plastic. The microbial synthesis of 3-HP has attracted significant attention in recent years due to its green and sustainable properties. In this paper, we provide an overview of the microbial synthesis of 3-HP from four major aspects, including the main 3-HP biosynthesis pathways and chassis strains used for the construction of microbial cell factories, the major carbon sources used for 3-HP production, and fermentation processes. Recent advances in the biosynthesis of 3-HP and related metabolic engineering strategies are also summarized. Finally, this article provides insights into the future direction of 3-HP biosynthesis.

Directed evolution of tripartite ATP-independent periplasmic transporter for 3-Hydroxypropionate biosynthesis

Our previous study's introduction of the malonic acid assimilation pathway into Escherichia coli enabled biosynthesis of 3-Hydroxypropionate (3-HP) from malonate. However, the relatively low uptake activity of tripartite ATP-independent periplasmic (TRAP) malonic acid transporter (MatPQM) is considered rate-limiting in malonate utilization. Here, to improve the transport performance of this importer, MatP variants were obtained via directed evolution and a novel developed enzyme-inhibition-based high throughput screening approach. This plate chromogenic screening method is based on the fact that malonic acid inhibits both of succinate dehydrogenase activity and further the capability of the reduction of methylene-blue to methylene-white. The best mutant E103G/S194G/Y218H/L235P/N272S showed twofold increased transport efficiency compared to the wild-type. ITC assay and structural analysis revealed that increased binding affinity of the mutant to the ligand was the reason for improved uptake activity of MatPQM. Finally, the engineered strain harboring the evolved mutant produced 20.08 g/L 3-HP with the yield of 0.87 mol/mol malonate in a bioreactor. Therefore, the well-established directed evolution strategy can be regarded as the reference work for other TRAP-type transporters engineering. And, this transporter mutant with enhanced malonic acid uptake activity has broad applications in the microbial biosynthesis of malonyl-CoA-derived valuable compounds in bacteria. KEY POINTS: • We reported directed evolution of a TRAP-type malonic acid transporter. • We found the enhanced malonate uptake activity of mutant lies in improved affinity. • We enhanced 3-HP bioproduction with high yield by employing the best mutant.

Dynamic and balanced regulation of the thrABC operon gene for efficient synthesis of L-threonine

L-threonine is an essential amino acid used widely in food, cosmetics, animal feed and medicine. The thrABC operon plays an important role in regulating the biosynthesis of L-theronine. In this work, we systematically analyzed the effects of separating thrAB and thrC in different proportions on strain growth and L-threonine production in Escherichia coli firstly. The results showed that higher expression of thrC than thrAB enhanced cell growth and L-threonine production; however, L-threonine production decreased when the thrC proportion was too high. The highest L-threonine production was achieved when the expression intensity ratio of thrAB to thrC was 3:5. Secondly, a stationary phase promoter was also used to dynamically regulate the expression of engineered thrABC. This strategy improved cell growth and shortened the fermentation period from 36 h to 24 h. Finally, the acetate metabolic overflow was reduced by deleting the ptsG gene, leading to a further increase in L-threonine production. With these efforts, the final strain P _2.1 -2901ΔptsG reached 40.06 g/L at 60 h fermentation, which was 96.85% higher than the initial control strain TH and the highest reported titer in shake flasks. The maximum L-threonine yield and productivity was obtained in reported fed-batch fermentation, and L-threonine production is close to the highest titer (127.30 g/L). In this work, the expression ratio of genes in the thrABC operon in E. coli was studied systematically, which provided a new approach to improve L-threonine production and its downstream products.