Promoter engineering for high ectoine production in a lower saline medium by Halomonas hydrothermalis Y2

Objectives For the stress from fermenters, down-stream processing equipment, andwastewater treatment to be alleviated, lowering salt-dependence in the ectoine synthesis process is of great significance in the moderately halotolerant Halomonas hydrothermalis Y2. Results In H. hydrothermalis Y2, the sigma(70)- and sigma(38)-controlled promoters of ectA are predicted to be involved in the osmotic regulation of ectoine synthesis. By substituting the ectA promoter with a promoter P-265 that identified in the outer membrane pore protein E of H. hydrothermalis Y2, the salt dependence of ectoine synthesis was significantly decreased. In the 500-ml flask containing various NaCl contents, the engineered strain (p/Y2/Delta ectD/Delta doeA) showed a remarkably enhanced ability in ectoine synthesis, especially under lower saline stress. After a 36-h fedbatch fermentation in the 1-l fermenter, p/Y2/Delta ectD/Delta doeA synthesized 11.5 g ectoine l(-1) in the presence of 60 g NaCl-1 l, with a high 0.32 g ectoine l(-1) h(-1) productivity, a specific productivity of 512.2 mg ectoine per g cell dry weight (CDW)(-1), and an excretion ratio of 67 % ectoine. Conclusions As no impaired growth was observed in strain p/Y2/Delta ectD/Delta doeA while ectoine synthesis was increased, this promoter engineering strategy provides a practical protocol for lowering the saltdependence of ectoine synthesis in this moderately halotolerant strain.

Automated summary

Lowering the salt dependence in ectoine synthesis process in Halomonas hydrothermalis Y2 can significantly enhance ectoine productivity under low saline stress, providing a practical protocol for strain improvement.