Ectoine Production Using Novel Heterologous EctABCS. salarius from Marine Bacterium Salinicola salarius

Ectoine, a heterocyclic amino acid produced by various bacteria, was widely used in the fields of cosmetics and medicine. In this study, a novel ectoine synthesis cluster from marine bacterium Salinicola salarius 1A01339 was firstly introduced into Escherichia coli BL21(DE3) for heterologous production of ectoine. The bioinformatic analysis proved the function of these ectoine synthesis enzymes, and showed the highest identities of 83.3–87.7% with enzymes from other microorganisms. Using the whole-cell biocatalytic method, 3.28 g/L ectoine was synthesized and excreted into the medium with the substrate of 200 mM sodium aspartate at 25 °C, pH 6.5 in flask-level. Further bioconversion was performed in the fermentor system at the high cell density of 20 OD/mL, and the concentration of extracellular ectoine was increased to 22.5 g/L in 24 h (equivalent to the specific productivity of 0.94 g/L·h), achieving over 6 times of production compared with that in flasks. Significantly, the recombinant strain demonstrated a lower catalytic temperature with the optimum of 25 °C, and a stronger tolerance to the substrate aspartate of 300 mM. These results might provide a compelling case for ectoine synthesis as well as potential applications in large-scale industrial production.

Metabolic Engineering of Escherichia Coli for Ectoine Production With the Fermentation Strategy of Supplementing Amino Donor

Background: Ectoine, a compatible solute, has broad application prospects in food biotechnology, agriculture, medicine, and cosmetics because of its protective action on biological compounds. Industrially, ectoine is produced by halophilic bacteria in a complex process. Recently, various works focus on improving ectoine production by using engineered strains, but there are still problems of low yield and low ectoine production efficiency.Results: To overcome the drawback, a final metabolic engineered strain E. coli ET08 was constructed by eliminating lysine synthesis branch and by-product metabolic pathways, and ectoine production reached 10.2 g/L through culture medium optimization. Compared with nitrate, addition of ammonium salt contributed more to the ectoine synthesis. Furthermore, the ammonium sulphate boosted more ectoine titers than ammonium chloride and sodium glutamate. The analysis of transcriptional levels revealed that the ammonium sulfate enhanced ectoine biosynthesis by enhancing metabolic flux toward ectoine biosynthesis and providing affluent synthetic precursors. Ultimately, the ectoine production and yield of the E. coli ET08 reached 36.5 g/L and 0.3 g/g glucose with supplementing amino donor in a 7.5 L bioreactor.Conclusions: a novel potential metabolic engineered Escherichia coli for ectoine production was constructed. optimizing amino donor and analyzing the transcription levels conclude that ammonium sulfate, as the optimal amino donor, has a positive effect on ectoine synthesis. It is the first report about the effect of exogenous amino donor on ectoine fermentation by metabolic engineered strain. The maximum ectoine production and yield from glucose synthesized by E. coli were obtained by two-stage feeding fermentation with supplementing amino donor. It provides a novel strategy for the synthesis of ectoine by engineered strain in industry. This research provides the basis for an effective process for ectoine production, together with the further applications of ectoine in food and cosmetics, and could also be used to produce other high value amino acid derivative.

Metabolic Engineering of Escherichia Coli for Ectoine Production with the Fermentation Strategy of Supplementing Amino Donor

Background: Ectoine, a compatible solute, has broad application prospects in food biotechnology, agriculture, medicine, and cosmetics because of its protective action on biological compounds. Industrially, ectoine is produced by halophilic bacteria in a complex process. Recently, various works focus on improving ectoine production by using engineered strains, but there are still problems of low yield and low ectoine production efficiency.Results: To overcome the drawback, a final metabolic engineered strain E. coli ET08 was constructed by eliminating lysine synthesis branch and by-product metabolic pathways, and ectoine production reached 10.2 g/L through culture medium optimization. Compared with nitrate, addition of ammonium salt contributed more to the ectoine synthesis. Furthermore, the ammonium sulphate boosted more ectoine titers than ammonium chloride and sodium glutamate. The analysis of transcriptional levels revealed that the ammonium sulfate enhanced ectoine biosynthesis by enhancing metabolic flux toward ectoine biosynthesis and providing affluent synthetic precursors. Ultimately, the ectoine production and yield of the E. coli ET08 reached 36.5 g/L and 0.3 g/g glucose with supplementing amino donor in a 7.5 L bioreactor.Conclusions: a novel potential metabolic engineered Escherichia coli for ectoine production was constructed. optimizing amino donor and analyzing the transcription levels conclude that ammonium sulfate, as the optimal amino donor, has a positive effect on ectoine synthesis. It is the first report about the effect of exogenous amino donor on ectoine fermentation by metabolic engineered strain. The maximum ectoine production and yield from glucose synthesized by E. coli were obtained by two-stage feeding fermentation with supplementing amino donor. It provides a novel strategy for the synthesis of ectoine by engineered strain in industry. This research provides the basis for an effective process for ectoine production, together with the further applications of ectoine in food and cosmetics, and could also be used to produce other high value amino acid derivative.

High ectoine production by an engineered Halomonas hydrothermalis Y2 in a reduced salinity medium

Background As an attracted compatible solute, 1,4,5,6-tetrahydro-2-methyl-4-pyrimidinecarboxylic acid (ectoine) showed great potentials in various field. However, lower productivity and high saline medium seriously hinder its wide applications. Results The entire ectoine metabolism, including pathways for ectoine synthesis and catabolism, was identified in the genome of an ectoine-excreting strain Halomonas hydrothermalis Y2. By in-frame deletion of genes encoding ectoine hydroxylase (EctD) and (or) ectoine hydrolase (DoeA) that responsible for ectoine catabolism, the pathways for ectoine utilization were disrupted and resulted in an obviously enhanced productivity. Using an optimized medium containing 100 g L−1 NaCl in a 500-mL flask, the double mutant of Y2/ΔectD/ΔdoeA synthesized 3.13 g L−1 ectoine after 30 h cultivation. This is much higher than that of the wild type strain (1.91 g L−1), and also exceeds the production of Y2/ΔectD (2.21 g L−1). The remarkably enhanced accumulation of ectoine by Y2/ΔectD/ΔdoeA implied a critical function of Doe pathway in the ectoine catabolism. Furthermore, to reduce the salinity of fermentation medium and overcome the wastewater treatment difficulty, mutants that lacking key Na+/H+ antiporter, Mrp and (or) NhaD2, were constructed based on strain Y2/ΔectD/ΔdoeA. As a result, the Mrp-deficient strain could synthesize equal amount of ectoine (around 7 g L−1 or 500 mg (g DCW) −1) in the medium containing lower concentration of NaCl. During a fed-batch fermentation process with 60 g L−1 NaCl stress, a maximum 10.5 g L−1 ectoine was accumulated by the Mrp-deficient strain, with a specific production of 765 mg (g DCW)−1 and a yield of 0.21 g g−1 monosodium glutamate. Conclusion The remarkably enhanced production of ectoine by Y2/ΔectD/ΔdoeA implied the critical function of Doe pathway in the ectoine catabolism. Moreover, the reduced salinity requirement of Mrp-deficient strain implied a feasible protocol for many compatible solute biosynthesis, i.e., by silencing some Na+/H+ antiporters in their halophilic producers and thus lowering the medium salinity.