Transcriptomic responses of haloalkalitolerant bacterium Egicoccus halophilus EGI 80432 to highly alkaline stress.

The haloalkalitolerant bacterium Egicoccus halophilus EGI 80432 exhibits high adaptability to saline-alkaline environment. The salinity adaptation mechanism of E. halophilus EGI 80432 was fully understood based on transcriptome analyses and physiological responses; however, the alkaline response mechanism has not yet been investigated. Here, we investigated the alkaline response mechanism of E. halophilus EGI 80432 by a transcriptomic comparison. In this study, the genes involved in the glycolysis, TCA cycle, starch, and trehalose metabolism for energy production and storage, were up-regulated under highly alkaline condition. Furthermore, genes responsible for the production of acidic and neutral metabolites, i.e., acetate, pyruvate, formate, glutamate, threonine, and ectoine, showed increased expression under highly alkaline condition, compared with the control pH condition. In contrast, the opposite results were observed in proton capture or retention gene expression profiles, i.e., cation/proton antiporters and ATP synthases. The above results revealed that E. halophilus EGI 80432 likely tended to adopt an "acidic metabolites production" strategy in response to a highly alkaline condition. These findings would pave the way for further studies in the saline-alkaline adaptation mechanisms of E. halophilus EGI 80432, and hopefully provide a new insight into the foundational theory and application in ecological restoration with saline-alkaline strains.