Genetic Control and Mechanisms of Salt and Hyperosmotic Stress Resistance in Cyanobacteria

Exposure to high concentrations of environmental NaCl exerts two stress effects on living cells, increasing the osmotic pressure and the concentration of inorganic ions. Salt stress dramatically suppresses the photosynthetic activity in cells of phototrophic organisms, such as cyanobacteria. During salt adaptation, cyanobacterial cells accumulate osmoprotectors, export excessive Na+ with the help of Na+/H+ antiporters, and actively absorb K+ with the help of K+-transporting systems. These physiological processes are accompanied by induction or suppression of several genes involved in salt adaptation. The review considers the main mechanisms responsible for the resistance of cyanobacterial cells to salt and hyperosmotic stresses. Special emphasis is placed on recent achievements in studying the genetic control of salt resistance and regulation of gene expression during adaptation of cyanobacteria to salt and hyperosmotic stresses.