Salts and brines

Summary: Cyanobacteria form a major component of the biota of hypersaline environments including salt lakes, solar salterns, hypersaline lagoons, and hypersaline sulphur springs. Cyanobacteria are often found in evaporite crusts of gypsum and even halite. A wide range of species were reported to live at high salinities. In many hypersaline environments cyanobacteria are exposed to high sulphide concentrations. Certain species are able to use sulphide as an electron donor in an anoxygenic type of photosynthesis through a process which involves photosystem I only. To be able to withstand the high osmotic pressure caused by the salt concentrations in their surrounding medium, cyanobacteria living at high salinities possess mechanisms to maintain osmotic equilibrium and cell turgor. Ions can temporarily enter the cells to counteract rapid increases in medium salinity. For long-term osmotic stabilization organic solutes are accumulated: the disaccharides sucrose and trehalose, glucosylglycerol, and glycine betaine. Molecular analysis of glucosylglycerol metabolism in Synechocystis PCC 6803 has greatly increased our insight into osmoregulatory mechanisms. Understanding the molecular mechanisms of osmotic adaptation in cyanobacteria has led to the exploration of a number of interesting biotechnological applications.