MpADC, an L-aspartate-α-decarboxylase, from Myzus persicae, that enables production of ß-alanine with high yield by whole-cell enzymatic catalysis.

BACKGROUND: ß-Alanine is a precursor of many important pharmaceutical products and food additives, its market demand is continuously increasing nowadays. Whole-cell catalysis relying on the recombinant expression of key ß-alanine synthesizing enzymes is an important method to produce ß-alanine. Nevertheless, ß-alanine synthesizing enzymes found so far have problems including easy inactivation, low expression or poor catalytic activity, and it remains necessary to develop new enzymes. RESULTS: Herein, we characterized an L-aspartate-α-decarboxylase, MpADC, from an aphid, Myzus persicae. It showed excellent catalytic activity at pH 6.0-7.5 and 37 °C. With the help of chaperone co-expression and N-terminal engineering guided by AlphaFold2 structure prediction, the expression and catalytic ability of MpADC in Escherichia coli were significantly improved. Using 50 g/L of E. coli cells expressing the MpADC-∆39 variant cultured in a 15-L fermenter, 232.36 g/L of ß-alanine was synthesized in 13.5 h, with the average ß-alanine yield of 17.22 g/L/h, which is best known so far. CONCLUSIONS: Our research should facilitate the production of ß-alanine in an environment-friendly manner.

Highly efficient production of ectoine via an optimized combination of precursor metabolic modules in Escherichia coli BL21.

Ectoine is an osmotic pressure protectant observed in various microorganisms and is widely used in cosmetics and pharmaceuticals. The market value of ectoine has increased considerably with social progress, resulting in high demand for ectoine production technology. Herein, a microbial cell factory in Escherichia coli that produces ectoine at high titers is described as developing efficient and environmentally friendly bio-based ectoine production technology. The ectoine biosynthetic pathway of Halomonas hydrothermalis was introduced into E. coli BL21 (DE3). Subsequent overexpression of precursor metabolic modules, including aspartate branching, pyruvate-oxoacetate, and glutamate biosynthesis pathways, resulted in the final strain, E. coli BCT08, which produced ectoine at a titer of 36.58 g/L during 30 h of fermentation. Sugar feeding speed optimization improved the ectoine titer to 131.8 g/L after 96 h of cultivation. This represents a remarkable achievement in ectoine production from glucose under low-salt conditions and has vast potential for industrial applications.

Improved paclitaxel delivery with PEG-b-PLA/zein nanoparticles prepared via flash nanoprecipitation.

Polymeric micelle is a promising vehicle to improve the bioavailability and clinical outcomes of paclitaxel (PTX) which has been proven effective in the treatment of a wide range of cancers. However, conventional PTX formulation with the amphiphilic PEG-b-PLA usually suffers from insufficient PTX loading, low stability of PTX-micelles, and rapid PTX release due to low compatibility between PTX and PLA, limiting its clinical application. In this study, a novel nanoparticle platform was developed to improve the stability of PTX-loaded nanoparticles (NPs) and the delivery efficacy of PTX by integrating the flash nanoprecipitation (FNP) technique and a combination of amphiphilic PEG-PLA and super hydrophobic zein. The incorporation of zein led to the formation of distinct hydrophobic interiors of NPs which enhanced the interaction between PTX and NPs, therefore improving the encapsulation efficiency of PTX and sustained drug release compared with PEG-PLA micelles without zein. In addition, FNP allowed facile fabrication of PTX-NPs with smaller sizes and higher stability. These PTX-NPs showed superior sustained release of PTX and good cancer cell-killing in vitro. Among them, PTX-5k-16k-1Z NPs exhibited excellent biosafety and anti-tumor efficacy in a xenograft tumor model in mice, suggesting great potential in the delivery of hydrophobic drugs for cancer therapy.

Modular reconstruction and optimization of the trans-4-hydroxy-L-proline synthesis pathway in Escherichia coli.

BACKGROUND: In recent years, there has been a growing demand for microbial production of trans-4-hydroxy-L-proline (t4Hyp), which is a value-added amino acid and has been widely used in the fields of medicine, food, and cosmetics. In this study, a multivariate modular metabolic engineering approach was used to remove the bottleneck in the synthesis pathway of t4Hyp. RESULTS: Escherichia coli t4Hyp synthesis was performed using two modules: a α-ketoglutarate (α-KG) synthesis module (K module) and L-proline synthesis with hydroxylation module (H module). First, α-KG attrition was reduced, and then, L-proline consumption was inhibited. Subsequently, to improve the contribution to proline synthesis with hydroxylation, optimization of gene overexpression, promotor, copy number, and the fusion system was performed. Finally, optimization of the H and K modules was performed in combination to balance metabolic flow. Using the final module H1K4 in a shaking flask culture, 8.80 g/L t4Hyp was produced, which was threefold higher than that produced by the W0 strain. CONCLUSIONS: These strategies demonstrate that a microbial cell factory can be systematically optimized by modular engineering for efficient production of t4Hyp.

N-acylhomoserine lactonase-based hybrid nanoflowers: a novel and practical strategy to control plant bacterial diseases.

BACKGROUND: The disease caused by plant pathogenic bacteria in the production, transportation, and storage of many crops has brought huge losses to agricultural production. N-acylhomoserine lactonases (AHLases) can quench quorum-sensing (QS) by hydrolyzing acylhomoserine lactones (AHLs), which makes them the promising candidates for controlling infections of QS-dependent pathogenic bacteria. Although many AHLases have been isolated and considered as a potentially effective preventive and therapeutic agents for bacterial diseases, the intrinsically poor ambient stability has seriously restricted its application. RESULTS: Herein, we showed that a spheroid enzyme-based hybrid nanoflower (EHNF), AhlX@Ni3(PO4)2, can be easily synthesized, and it exhibited 10 times AHL (3OC8-HSL) degradation activity than that with free AhlX (a thermostable AHL lactonase). In addition, it showed intriguing stability even at the working concentration, and retained ~ 100% activity after incubation at room temperature (25 °C) for 40 days and approximately 80% activity after incubation at 60 °C for 48 h. Furthermore, it exhibited better organic solvent tolerance and long-term stability in a complicated ecological environment than that of AhlX. To reduce the cost and streamline production processes, CSA@Ni3(PO4)2, which was assembled from the crude supernatants of AhlX and Ni3(PO4)2, was synthesized. Both AhlX@Ni3(PO4)2 and CSA@Ni3(PO4)2 efficiently attenuated pathogenic bacterial infection. CONCLUSIONS: In this study, we have developed N-acylhomoserine lactonase-based hybrid nanoflowers as a novel and efficient biocontrol reagent with significant control effect, outstanding environmental adaptability and tolerance. It was expected to overcome the bottlenecks of poor stability and limited environmental tolerance that have existed for over two decades and pioneered the practical application of EHNFs in the field of biological control.

Comparative Transcriptome Analysis Demonstrates the Positive Effect of the Cyclic AMP Receptor Protein Crp on Daptomycin Biosynthesis in Streptomyces roseosporus.

Daptomycin, which is produced by Streptomyces roseosporus, has been characterized as a novel cyclic lipopeptide antibiotic that is effective against Gram-positive bacteria. The biosynthesis of daptomycin is regulated by various factors. In the present study, we demonstrated that the cyclic AMP receptor protein (Crp) plays an important role in producing daptomycin in the S. roseosporus industrial strain. We found that daptomycin production from the crp deletion strain decreased drastically, whereas production from the crp overexpression strain increased by 22.1%. Transcriptome and qPCR analyses showed that some genes related to the daptomycin biosynthetic gene cluster (dpt) and the pleiotropic regulator (adpA) were significantly upregulated. RNA-seq also shows Crp to be a multifunctional regulator that modulates primary metabolism and enhances precursor flux to secondary metabolite biosynthesis. These results provide guidance for the development and improvement of potential natural products.

Metabolic engineering strategy for synthetizing trans-4-hydroxy-L-proline in microorganisms.

Trans-4-hydroxy-L-proline is an important amino acid that is widely used in medicinal and industrial applications, particularly as a valuable chiral building block for the organic synthesis of pharmaceuticals. Traditionally, trans-4-hydroxy-L-proline is produced by the acidic hydrolysis of collagen, but this process has serious drawbacks, such as low productivity, a complex process and heavy environmental pollution. Presently, trans-4-hydroxy-L-proline is mainly produced via fermentative production by microorganisms. Some recently published advances in metabolic engineering have been used to effectively construct microbial cell factories that have improved the trans-4-hydroxy-L-proline biosynthetic pathway. To probe the potential of microorganisms for trans-4-hydroxy-L-proline production, new strategies and tools must be proposed. In this review, we provide a comprehensive understanding of trans-4-hydroxy-L-proline, including its biosynthetic pathway, proline hydroxylases and production by metabolic engineering, with a focus on improving its production.

Optimization of fermentation conditions and medium compositions for the production of chrysomycin a by a marine-derived strain Streptomyces sp. 891.

Chrysomycin A is one of the valuable drug leads used to treat infectious diseases such as tuberculosis and methicillin-resistant Staphylococcus aureus. In order to increase its yield, this work firstly focuses on optimization of fermentation conditions and medium compositions of a wild-type chrysomycin A-producing strain Streptomyces sp. 891 from marine sediment. By single-factor experiment, effects of fermentation conditions (fermentation time, seed age, initial pH, inoculum amount, liquid loading, shaking speed) and medium composition (carbon sources, nitrogen sources, inorganic salts) on the yield of chrysomycin A were carefully evaluated and analyzed followed by optimization at shake-flask level. The results indicated its optimal fermentation conditions for producing chrysomycin A were as follows: fermentation time 168 h, seed age 48 h, initial pH 6.5, inoculum amount 5.0%, liquid loading 30 mL in 250-mL Erlenmeyer flask and shaking speed 220 rpm. By orthogonal test, the optimal fermentation medium constitutes 40 g/L glucose, 20 g/L corn starch, 25 g/L hot-pressed soybean flour, 3 g/L CaCO3. Verification tests suggested the yield of chrysomycin A under optimized conditions reaches up to 3648 ± 119 mg/L, which is increased by almost 5 times. These findings definitely pave the way for scale-up preparation of chrysomycin A and application in the pharmaceutical industry.

Metabolic Pathway Construction and Optimization of Escherichia coli for High-Level Ectoine Production.

Ectoine is widely produced by various bacteria as a natural cell protectant against environment stress, e.g., osmotic and temperature stress. Its protective properties therefore exhibit high commercial value, especially in agriculture, medicine, cosmetics, and biotechnology. Here, we successfully constructed an engineered Escherichia coli for the heterologous production of ectoine. Firstly, the ectABC genes from Halomonas elongata were introduced into E. coli MG1655 to produce ectoine without high osmolarity. Subsequently, lysA gene was deleted to weaken the competitive L-lysine biosynthesis pathway and ectoine bioconversion was further optimized, leading to an increase of ectoine titer by 16.85-fold. Finally, at the low cell density of 5 OD600/mL in Erlenmeyer flask, the concentration of extracellular ectoine was increased to 3.05 mg/mL. At the high cell density of 15 OD600/mL, 12.7 g/L of ectoine was achieved in 24 h and the overall yield is 1.27 g/g glycerol and sodium aspartate. Our study herein provides a feasible and valuable biosynthesis pathway of ectoine with a potential for large-scale industrial production using simple and cheap feedstocks.

Phosphate regulator PhoP directly and indirectly controls transcription of the erythromycin biosynthesis genes in Saccharopolyspora erythraea.

BACKGROUND: The choice of phosphate/nitrogen source and their concentrations have been shown to have great influences on antibiotic production. However, the underlying mechanisms responsible for this remain poorly understood. RESULTS: We show that nutrient-sensing regulator PhoP (phosphate regulator) binds to and upregulates most of genes (ery cluster genes) involved in erythromycin biosynthesis in Saccharopolyspora erythraea, resulting in increase of erythromycin yield. Furthermore, it was found that PhoP also directly interacted with the promoter region of bldD gene encoding an activator of erythromycin biosynthesis, and induced its transcription. Phosphate limitation and overexpression of phoP increased the transcript levels of ery genes to enhance the erythromycin production. The results are further supported by observation that an over-producing strain of S. erythraea expressed more PhoP than a wild-type strain. On the other hand, nitrogen signal exerts the regulatory effect on the erythromycin biosynthesis through GlnR negatively regulating the transcription of phoP gene. CONCLUSIONS: These findings provide evidence that PhoP mediates the interplay between phosphate/nitrogen metabolism and secondary metabolism by integrating phosphate/nitrogen signals to modulate the erythromycin biosynthesis. Our study reveals a molecular mechanism underlying antibiotic production, and suggests new possibilities for designing metabolic engineering and fermentation optimization strategies for increasing antibiotics yield.

AhlX, an N-acylhomoserine Lactonase with Unique Properties.

N-Acylhomoserine lactonase degrades the lactone ring of N-acylhomoserine lactones (AHLs) and has been widely suggested as a promising candidate for use in bacterial disease control. While a number of AHL lactonases have been characterized, none of them has been developed as a commercially available enzymatic product for in vitro AHL quenching due to their low stability. In this study, a highly stable AHL lactonase (AhlX) was identified and isolated from the marine bacterium Salinicola salaria MCCC1A01339. AhlX is encoded by a 768-bp gene and has a predicted molecular mass of 29 kDa. The enzyme retained approximately 97% activity after incubating at 25 °C for 12 days and ~100% activity after incubating at 60 °C for 2 h. Furthermore, AhlX exhibited a high salt tolerance, retaining approximately 60% of its activity observed in the presence of 25% NaCl. In addition, an AhlX powder made by an industrial spray-drying process attenuated Erwinia carotovora infection. These results suggest that AhlX has great potential for use as an in vitro preventive and therapeutic agent for bacterial diseases.

Metabolic engineering of Corynebacterium glutamicum S9114 to enhance the production of l-ornithine driven by glucose and xylose.

l-ornithine, an important amino acid, is widely used in food and medicine industries. l-ornithine production mainly relies on microbial fermentation, which may not meet the industrial requirement owing to the poor fermentation ability of available strains. Herein, mscCG2 deletion, CgS9114_12202 (gdh2) overexpression and rational modulation in tricarboxylic acid cycle was firstly demonstrated to increase l-ornithine production in engineered Corynebacterium glutamicum S9114. By further modulate glucose utility result in strain SO26 that produced 38.5 g/L or 43.6 g/L of l-ornithine in shake flask and fed-batch fermentation, respectively. This was 25% higher than that of the original strain (30.8 g/L) and exhibits highest titer reported in shake-flask. Moreover, the incorporation of xylose pathway in the engineered strain resulted in the highest l-ornithine production titer (18.9 g/L) and yield (0.40 g/g xylose) with xylose substrate. These results illustrate the tremendous potential of the engineered strain C. glutamicum S9114 in l-ornithine production.

[Determination of aminobutanol by high performance liquid chromatography based on charge transfer reaction].

A method was developed for the determination of the content of aminobutanol by high performance liquid chromatography (HPLC) based on charge transfer reaction. Under the condition of a borax-boric acid buffer solution of pH 8.4, aminobutanol and tetra-chloro-benzoquinone reacted at 60℃ for 60 min, and were analyzed by an HPLC-ultraviolet detector. The charge-transfer complex was separated on an Agilent Extend C18 column (250 mm×4.6 mm, 5 µm) with 0.001% (v/v) triethylamine and methanol as the mobile phases for gradient elution at a flow rate of 1 mL/min. The limit of quantification of aminobutanol was 0.01 g/L, the linear range was 0.1-0.6 g/L, and the correlation coefficient (R2) was 0.9994. The spiked recoveries of the method were 98.3%-103.6% with relative standard deviations (RSDs) of 0.9%-1.6%. The method is simple and quick, and suitable for the rapid detection of aminobutanol.

Protein Acylation is a General Regulatory Mechanism in Biosynthetic Pathway of Acyl-CoA-Derived Natural Products.

Coenzyme A (CoA) esters of short fatty acids (acyl-CoAs) function as key precursors for the biosynthesis of various natural products and the dominant donors for lysine acylation. Herein, we investigated the functional interplay between beneficial and adverse effects of acyl-CoA supplements on the production of acyl-CoA-derived natural products in microorganisms by using erythromycin-biosynthesized Saccharopolyspora erythraea as a model: accumulation of propionyl-CoA benefited erythromycin biosynthesis, but lysine propionylation inhibited the activities of important enzymes involved in biosynthetic pathways of erythromycin. The results showed that the overexpression of NAD+-dependent deacylase could circumvent the inhibitory effects of high acyl-CoA concentrations. In addition, we demonstrated the similar lysine acylation mechanism in other acyl-CoA-derived natural product biosynthesis, such as malonyl-CoA-derived alkaloid and butyryl-CoA-derived bioalcohol. These observations systematically uncovered the important role of protein acylation on interaction between the accumulation of high concentrations of acyl-CoAs and the efficiency of their use in metabolic pathways.

Protein Acylation Affects the Artificial Biosynthetic Pathway for Pinosylvin Production in Engineered E. coli.

The effect of regulatory system on the engineered biosynthetic pathway in chassis cells remains incompletely understood in microorganisms. Acyl-CoAs function as key precursors for the biosynthesis of various natural products and the dominant donors for protein acylation. The polyphenol pinosylvin, with high antimicrobial and antifungal activities, is biosynthesized with malonyl-CoA as its direct precursors. But correlation between lysine malonylation and pinosylvin biosynthesis remains unknown. Herein, we found that the malonyl-CoA-driven lysine malonylation plays an important role in interaction between the engineered pathway of pinosylvin synthesis and E. coli chassis cell. Oversupply of malonyl-CoA leads to an increase in malonylation level of global proteome as well as the enzymes in the artificial pathway, thereby decreasing yield of pinosylvin. The results revealed that the intricate balance of cellular acyl-CoA concentrations is critical for the yields of acyl-CoA-derived natural products. We next modified the enzymes in the biosynthetic pathway to adjust their acylation level and successfully improved the yield of pinosylvin. Our study uncovers the effect of protein acylation on the biosynthetic pathway, helps optimization of synthetic constructs, and provides new strategies in metabolic engineering and synthetic biology at the protein post-translational level.