Exploring useful fermentation strategies for the production of hydroxyectoine with a halophilic strain, Halomonas salina BCRC 17875.

Hydroxyectoine, an ectoine derivative, is the most common compatible solute in halophilic microorganisms for resisting harsh environments. Compatible solutes can be utilized in fields such as cosmetics, medicine, and biochemistry. Moderately halophilic microorganisms produce much less hydroxyectoine as compared with ectoine. In this study, we first evaluate the effect of medium formulation (i.e., yeast extract (YE) medium and high yeast extract (HYE) medium) on hydroxyectoine production. In addition, an investigation of hydroxyectoine production by Halomonas salina under optimal conditions for vital factors (i.e., iron and α-ketoglutarate) and hydroxylase activity was also carried out. As a result, hydroxyectoine production was obviously elevated (0.9 g/L to 1.8 g/L) when the HYE medium was utilized. Furthermore, hydroxyectoine production further increased to 2.4 g/L when both the α-ketoglutarate and iron factors were added to the HYE medium in the early stationary phase. In addition, we found that ectoine hydroxylase activity increased more when a combination of iron and α-ketoglutarate was used than when either was used alone. The results showed that the alteration of iron and α-ketoglutarate clearly stimulated the expression of ectoine hydroxylase, which in turn affected hydroxyectoine synthesis. This study also showed that hydroxyectoine production was further raised from 2.4 g/L to 2.9 g/L when 50 mM of α-ketoglutarate and 1 mM of iron were added to the HYE medium. Ultimately, the experimental results showed using the optimal conditions further elevated the hydroxyectoine production yield to 2.90 g/L, which was over 3-fold higher than the best results obtained from the original medium.