Optimization of ectoine production from Nesterenkonia xinjiangensis and one-step ectoine purification

Microbial Production of Ectoine: A Review

Ectoine is an important natural secondary metabolite widely used in biomedical fields, novel cosmetics development, and the food industry. Due to the increasing market demand for ectoine, more cost-effective production methods are being explored. With the rapid development of synthetic biology and metabolic engineering technologies, the production of ectoine using traditional halophilic bacteria is gradually being replaced by higher-yielding and environmentally friendly nonhalophilic engineered strains. By introducing the ectoine synthesis pathway into model strains and optimizing the fermentation process through various metabolic regulations, high-level production of ectoine can be achieved. This review focuses on strategies for the microbial production of ectoine, including screening of wild strains, mutation breeding, and metabolic engineering of model strains, to elucidate the current research status and provide insights for the industrial production of ectoine.

Metabolic Engineering of Escherichia coli for Efficient Production of Ectoine

Ectoine is a valuable compatible solute with extensive applications in bioengineering, cosmetics, medicine, and the food industry. While certain halophilic bacteria can naturally produce ectoine, as a model organism for biomanufacturing, Escherichia coli offers significant advantages to be engineered for potentially high-level ectoine production. However, complex metabolic flux distributions and byproduct formation present bottlenecks that limit ectoine production in E. coli. In this study, we aimed to enhance ectoine production in E. coli BL21(DE3) through systematic metabolic engineering strategies. We investigated the effects of the ectABC gene cluster sequence, plasmid copy number, and key gene copy number on ectoine synthesis. Using the original ectABC sequence with the high-copy-number plasmid pRSFDuet-1 resulted in the highest level of ectoine production. Knocking out genes encoding homoserine dehydrogenase and diaminopimelate decarboxylase reduced competing pathways, further increasing ectoine yield. Overexpression of aspartate semialdehyde dehydrogenase, aspartate kinase I (thrA*), aspartate aminotransferase, and aspartate ammonia-lyase (aspA) was performed, and optimal gene copy numbers were determined. When the copy numbers of thrA* and aspA were both three, ectoine synthesis improved, reaching 1.91 g/L. Enhancing the oxaloacetate pool by overexpressing phosphoenolpyruvate carboxylase (ppc) or introducing pyruvate carboxylase (pyc) from Corynebacterium glutamicum further increased ectoine production to 4.99 g/L. Balancing NADPH and ATP levels through cofactor engineering contributed to additional production improvements. Combining these strain engineering strategies, we ultimately constructed strain C24, which produced 35.33 g/L ectoine in a 5 L fermenter with a glucose conversion rate of 0.21 g/g. These results demonstrate that targeted metabolic engineering can significantly enhance ectoine production in E. coli, providing a foundation for industrial-scale production.

The tropical marine actinomycete Nocardiopsis dassonvillei NCIM 5124 as novel source of ectoine: Genomic and transcriptomic insights

Since ectoine is a high-value product, overviewing strategies for identifying novel microbial sources becomes relevant. In the current study, by following a genome mining approach, the ectoine biosynthetic cluster in a tropical marine strain of Nocardiopsis dassonvillei (NCIM 5124) was located and compared with related organisms. Transcriptome analysis of Control and Test samples (with 0 and 5% NaCl, respectively) was carried out to understand salt induced stress response at the molecular level. There were 4950 differentially expressed genes with 25 transcripts being significantly upregulated in Test samples. NaCl induced upregulation of the ectoine biosynthesis cluster and some other genes (stress response, chaperone/Clp protease, cytoplasm, ribonucleoprotein and protein biosynthesis). The production of ectoine as a stress response molecule was experimentally validated via LCMS analysis. The investigation sheds light on the responses exhibited by this actinomycete in coping up with salt stress and provides a foundation for understanding salt induced molecular interactions.

High efficiency production of 5-hydroxyectoine using metabolically engineered Escherichia coli

The 5-hydroxyectoine is a natural protective agent with long-lasting moisturising and radiation resistance properties. It can be naturally synthesized by some extremophiles using the "bacterial milking" process, but this can corrode bioreactors and downstream purification may cause environmental pollution. In this study, an engineered Escherichia coli (E. coli) strain was constructed for the 5-hydroxyectoine production. First, three ectoine hydroxylases were characterised and the enzyme from Halomonas elongata was the most effective. The L-2,4-diaminobutyrate transaminase mutant was introduced into the engineered strain, which could accumulate 2.8 g/L 5-hydroxyectoine in shake flasks. By activating the glyoxylate cycle and balancing the α-ketoglutarate distribution, the 5-hydroxyectoine titer was further increased to 3.4 g/L. Finally, the optimized strain synthesized 58 g/L 5-hydroxyectoine via a semi-continuous feeding process in a NaCl-free medium. Overall, this study reported the highest titer of 5-hydroxyectoine synthesized by E. coli and established a low-salt fermentation process through the aforementioned efforts.

Investigation of Nitrogen Removal in Flue Gas Desulfurization and Denitrification Wastewater Utilizing Halophilic Activated Sludge

In the process of flue gas desulfurization and denitrification, the generation of high-sulfate wastewater containing nitrogen is a significant challenge for biological wastewater treatment. In this study, halophilic activated sludge was inoculated in a Sequencing Batch Reactor to remove nitrogen from wastewater with a high sulfate concentration (60 g/L). With the influent concentration of 180 mg/L, the removal rate of total nitrogen was more than 96.7%. The effluent ammonium nitrogen concentration was lower than 1.94 mg/L, and the effluent nitrate nitrogen and nitrite nitrogen concentrations were even lower than 0.77 mg/L. The salt tolerance of activated sludge is mainly related to the increase in the content of ectoine in microbial cells. The Specific Nitrite Oxidation Rate is quite low, while the Specific Nitrite Reduction Rate and Specific Nitrate Reduction Rate are relatively strong. In the system, there are various nitrogen metabolic processes, including aerobic nitrification, anaerobic denitrification, and simultaneous nitrification-denitrification processes. By analyzing the nitrogen metabolic mechanisms and microbial community structure of the reaction system, dominate bacteria can be identified, such as Azoarcus, Thauera, and Halomonas, which have significant nitrogen removal capabilities.

Elucidating the salt-tolerant mechanism of Halomonas cupida J9 and unsterile ectoine production from lignocellulosic biomass

BACKGROUND

Ectoine as an amino acid derivative is widely applied in many fields, such as the food industry, cosmetic manufacturing, biologics, and therapeutic agent. Large-scale production of ectoine is mainly restricted by the cost of fermentation substrates (e.g., carbon sources) and sterilization.

RESULTS

In this study, Halomonas cupida J9 was shown to be capable of synthesizing ectoine using xylose as the sole carbon source. A pathway was proposed in H. cupida J9 that synergistically utilizes both WBG xylose metabolism and EMP glucose metabolism for the synthesis of ectoine. Transcriptome analysis indicated that expression of ectoine biosynthesis module was enhanced under salt stress. Ectoine production by H. cupida J9 was enhanced by improving the expression of ectoine biosynthesis module, increasing the intracellular supply of the precursor oxaloacetate, and utilizing urea as the nitrogen source. The constructed J9U-P8EC achieved a record ectoine production of 4.12 g/L after 60 h of xylose fermentation. Finally, unsterile production of ectoine by J9U-P8EC from either a glucose-xylose mixture or corn straw hydrolysate was demonstrated, with an output of 8.55 g/L and 1.30 g/L of ectoine, respectively.

CONCLUSIONS

This study created a promising H. cupida J9-based cell factory for low-cost production of ectoine. Our results highlight the potential of J9U-P8EC to utilize lignocellulose-rich agriculture waste for open production of ectoine.

Sugar beet molasses: a sweet solution for ectoine production by Nesterenkonia sp

Ectoine, a biologically significant compound, was successfully produced by a strain of bacteria capable of utilizing sucrose. In a ground-breaking approach, we harnessed the potential of sugar beet molasses, a by-product rich in sucrose, amino acid, and vitamins, as a growth medium for this purpose. Through meticulous investigation, we identified the ideal conditions for maximizing ectoine synthesis. This remarkable milestone was reached by introducing only 1 g of (NH₄)₂SO₄ and 5 mL of molasses per liter, maintaining a pH level of 8.0, upholding a 7.5% NaCl concentration, employing agitation at 120 rpm, and sustaining a temperature of 30 °C. This study marks a pioneering endeavour as it represents the first instance where molasses has been effectively employed to produce ectoine through the cultivation of Nesterenkonia sp. We showcased the production of 75.56 g of the valuable compound ectoine utilizing 1 L of waste molasses with this specific bacterial strain. These findings hold tremendous promise, not only in terms of resource utilization but also for the potential applications of ectoine in various biological contexts.

Ectoine production from a novel bacterial strain and high-purity purification with a cost-effective and single-step method

This study marks the exploration into the production of ectoine, a valuable compound with significant potential as an antioxidant, osmoprotectant, anti-inflammatory agent, and stabilizer of cell membranes, proteins, and DNA integrity. Our focus centred on investigating the presence of ectoine and optimizing its production by the novel ectoine producer bacterial strain, Piscibacillus halophilus. For the optimization of ectoine production the effects of carbon and nitrogen sources, salt, pH, agitation and incubation period were optimized by one-factor-at-a-time. We started with an initial ectoine content of 46.92 mg/L, and through a series of optimization processes, we achieved a remarkable increase, resulting in an ectoine content of 1498.2 mg/L. The bacterial species P. halophilus achieved its highest ectoine production after 48 h of incubation, with conditions set at 10 % (w/v) salinity, pH of 7.50, and an agitation speed of 160 rpm. These precise conditions were found to be the most favourable for maximizing ectoine production by this strain. Besides, we have achieved successful purification of ectoine from the crude extract through a streamlined single-step process. This purification method has delivered an exceptional level of purity, surpassing 99.15 %, and an impressive yield of over 99 %. Importantly, we accomplished this using readily available and cost-effective strong acids (HCl) and strong bases (NaOH) to arrange pH gradients. The use of acid and base in the purification process of ectoine reflects an innovative and sustainable methodology.

Usage of ectoine as a cryoprotectant for cryopreservation of lactic acid bacteria

Streptococcus thermophilus, the only Streptococcus species considered "Generally Recognized Safe", has been used widely in the food industry. This bacterium is one of the most valuable industrial lactic acid bacterial species. Due to the importance of this bacterium in industrial applications, it should be stored for a long time without losing its metabolic properties. The present study aimed to investigate the cryoprotectant effect of three compatible solutes (ectoine, trehalose, and sucrose) on bacterial cells stored at different temperatures (frozen at -80 °C or freeze-dried and subsequently stored at +4, -20, and -80 °C) for three months. The bacterial cells were tested for cell viability, bile salt tolerance, and lactic acid production before and after processing. The highest cell viability, bile salt tolerance, and lactic acid production were obtained with ectoine and under frozen (storage at -80 °C) conditions. In freeze-dried and subsequently stored at various temperatures, the best preservation was obtained at -80 °C, followed by -20 °C and +4 °C. Moreover, when ectoine's preservation potential was compared to other cryoprotectants, ectoine showed the highest preservation, followed by trehalose and sucrose. Although ectoine has a variety of qualities that have been proven, in the current work, we have shown for the first time that ectoine has cryoprotectant potential in yogurt starter cultures (S. thermophilus).

Recent advances in production and applications of ectoine, a compatible solute of industrial relevance

Extremophilic bacteria growing in saline ecosystems are potential producers of biotechnologically important products including compatible solutes. Ectoine/hydroxyectoine are two such solutes that protect cells and associated macromolecules from osmotic, heat, cold and UV stress without interfering with cellular functions. Since ectoine is a high value product, overviewing strategies for improving yields become relevant. Screening of natural isolates, use of inexpensive substrates and response surface methodology approaches have been used to improve bioprocess parameters. In addition, genome mining exercises can aid in identifying hitherto unreported microorganisms with a potential to produce ectoine that can be exploited in the future. Application wise, ectoine has various biotechnological (protein protectant, membrane modulator, DNA protectant, cryoprotective agent, wastewater treatment) and biomedical (dermatoprotectant and in overcoming respiratory and hypersensitivity diseases) uses. The review summarizes current updates on the potential of microorganisms in the production of this industrially relevant metabolite and its varied applications.

Metabolic engineering combined with enzyme engineering for overproduction of ectoine in Escherichia coli

Ectoine, a natural protective agent, is naturally synthesized at low titers by some extreme environment microorganisms that are usually difficult to culture. There is a need for an efficient and eco-friendly ectoine production process. In this study, Escherichia coli BL21(DE3) with the ectABC gene cluster from Halomonas venusta achieved 1.7 g/L ectoine. After optimizing the expression plasmid, 2.1 g/L ectoine was achieved. Besides, the aspartate kinase mutant LysCT311I from Corynebacterium glutamicum and aspartate semialdehyde dehydrogenase from Halomonas elongata were overexpressed to increase precursors supply. Furthermore, the rate-limiting enzyme EctB was semirationally engineered, and the E407D mutation enhanced ectoine production by 13.8 %. To improve acetyl-CoA supply, the non-oxidative glycolysis pathway was introduced. Overall, the optimized strain ECT9-5 produced 67.1 g/L ectoine by fed-batch fermentation with a 0.3 g/g of glucose and the kinetic model resulted in a good fit.