Osmoadaptation of haloalkaliphilic bacteria: Role of osmoregulators and their possible practical application

The review discusses osmoadaptation of haloalkaliphilic bacteria from diverse taxonomic and physiological groups, inhabiting soda lakes. Our experimental research has confirmed the similarity of the osmoregulation strategies in neutrophilic and alkaliphilic halophiles, independent of their pH homeostasis mechanism. The external osmotic pressure is equilibrated either due to accumulation of ions from the environment, or by accumulation or synthesis of cytoplasmic osmoregulatory compounds. The alkaliphiles following the "compatible solutes" strategy contain low or moderate concentrations of salts in their cytoplasm; their proteins do not require adaptation to salts. Those that follow the "salt-in" strategy do not synthesize osmoregulators: they accumulate high levels of salts within the cell and thus equilibrate the osmotic pressures of the cell and the environment. The proteins of these bacteria contain more acidic amino acid residues compared to the proteins of neutrophiles. The functions of bacterial organic osmoregulatory compounds are discussed, as well as their characteristics of possible practical value. Applications for ectoine and betaine are discussed based on the published data.