Ectoine Production Using Novel Heterologous EctABC<i>_{S. salarius}</i> from Marine Bacterium <i>Salinicola salarius</i>

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 <i>Salinicola salarius</i> 1A01339 was firstly introduced into <i>Escherichia coli</i> 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.