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.