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

Abstract

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

Osmotic stress in Synechocystis sp. PCC 6803: low tolerance towards nonionic osmotic stress results from lacking activation of glucosylglycerol accumulation

“…For osmotic stress treatments the commonly used compound sorbitol was compared to maltose, which in contrast to sorbitol is a disaccharide. Neither sorbitol nor maltose are transported by the uptake system for osmoprotective compounds in Synechocystis (Mikkat et al, 1996). This study indicates that different extracellular and particular intracellular signals are perceived by Synechocystis cells during salt or osmotic stress conditions.…”

“…It is known that Synechocystis is able to take up the carbohydrates glucose (Schmetterer, 1990), GG, trehalose and sucrose. The latter three solutes are transported by the salt-regulated ABC-type transporter Ggt (Mikkat et al, 1996;Mikkat & Hagemann, 2000). Because the participation of this transporter in sorbitol uptake has been excluded (Mikkat et al, 1996), the transporter responsible for the uptake of this compand remains unknown.…”

“…The latter three solutes are transported by the salt-regulated ABC-type transporter Ggt (Mikkat et al, 1996;Mikkat & Hagemann, 2000). Because the participation of this transporter in sorbitol uptake has been excluded (Mikkat et al, 1996), the transporter responsible for the uptake of this compand remains unknown. We suggest that sorbitol is penetrating the cell membrane by facilitated diffusion, since the uptake rate depends on the external sorbitol concentration over a wide range.…”

“…The Na + ions, for example, are exported by Na + /H + antiporters (Inaba et al, 2001;Elanskaya et al, 2002), which are regulated at the activity level, since their gene expression does not change in salt-shocked cells (Marin et al, 2004). The internal osmotic potential of Synechocystis cells is balanced by uptake (Mikkat et al, 1996) or de novo synthesis Marin et al, 1998) of the compatible solute glucosylglycerol (GG), which enhances the internal osmotic potential, and is also able to directly protect proteins and membranes (Borges et al, 2002;Hincha & Hagemann, 2004). The synthesis of GG is regulated by a salt-dependent modulation of the activity of the key enzyme glucosylglycerolphosphate synthase (GgpS), as well as by an increased expression of all genes encoding proteins involved in GG synthesis during salt acclimatization (Hagemann & Erdmann, 1994;Kanesaki et al, 2002).…”

Trehalose and Abiotic Stress in Biological Systems

“…However, cyanobacteria use compatible solutes synthesized de novo and use the transporters to uptake their compatible solutes that have diffused into the periplasm (Hagemann, 2011). A transporter with uptake specificity for sucrose, trehalose and glucosylglycerol has been discovered for the first time in Synechocystis (Mikkat et al, 1996). The soil bacterium Corynebacterium glutamicum utilizes trehalose as a compatible solute depending on the environmental conditions.…”