Multiphasic osmotic adjustment in a euryhaline cyanobacterium

Transfer of Synechocystis PCC6714 from a freshwater medium to a saline medium caused the cells to shrink; rapid entry of NaCl resulted in a partial recovery of cellular volume within 2 min. Active extrusion of internal Na+ in exchange for extracellular K+ then occurred (within 20 min). Finally, the low‐Mr carbohydrates sucrose and glucosylglycerol were accumulated and internal KC1 levels declined. In long‐term growth experiments, the relative importance of sucrose as a component of the low‐Mr organic solute fraction decreased and glucosylglycerol became the single most important intracellular solute. These observations demonstrate that several inorganic and organic solutes are involved in osmotic adjustment in this cyanobacterium, with sequential changes in the relative importance of each solute following transfer to a saline medium.