Active transport of glucosylglycerol is involved in salt adaptation of the cyanobacterium Synechocystis sp strain PCC 6803

An active-transport system for the osmoprotective compound glucosylglycerol (GG) was found in the cyanobacterium Synechocystis sp. strain PCC 6803. Uptake assays with C-14-labelled CC showed that the CG transport was enhanced in cells adapted to increasing concentrations of NaCl. Kinetic studies indicated a Michaelis-Menten relationship, The uptake of CG was energy dependent and occurred against a steep concentration gradient. It was inhibited by uncouplers as well as by a combination of darkness and KCN. The affinity of the transporter seems to be restricted to osmoprotective compounds of cyanobacteria; from a variety of compounds tested only sucrose and trehalose competed with CG for uptake, A salt-sensitive mutant of Synechocystis 6803 unable to synthesize CG could be complemented to salt resistance by exogenous CC. Accumulation of CC from the medium was essential for the restoration of photosynthesis and growth in mutant cells under high-salt conditions, In wild-type cells, the CC transporter probably serves to prevent CC leaking out of salt-stressed cells.