Biotechnology Letters, Vol.43, No.4, 825-834, 2021
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.