Salt-Dependent Expression of Glucosylglycerol-Phosphate Synthase, Involved in Osmolyte Synthesis in the Cyanobacterium Synechocystis sp. Strain PCC 6803

Abstract

The cyanobacterium Synechocystis sp. strain PCC 6803 is able to acclimate to levels of salinity ranging from freshwater to twice the seawater concentrations of salt by accumulating the compatible solute glucosylglycerol (GG). Expression of the ggpS gene coding for the key enzyme (glucosylglycerol-phosphate synthase) in GG synthesis was examined in detail. Under control conditions, the GgpS protein is stable, so that weak constitutive transcription of the ggpS gene resulted in a significant protein content. However, the enzyme activity was biochemically switched off, and no GG was detectable. After a salt shock, an immediate increase in mRNA content proportional to the salt content occurred, while the GgpS protein and GG contents rose in a linear manner. Furthermore, the stability of the ggpS mRNA increased transiently. In salt-acclimated cells expression of the ggpS gene, the GgpS protein content, and the amount of accumulated GG depended linearly on the external salt concentration. Mapping of the 5 end of the ggpS transcript revealed a long nontranslated 5 sequence and a putative typical cyanobacterial promoter, which did not show any obvious salt-regulatory element. The alternative factor F was found to be involved in salt-dependent regulation of ggpS, since in a F mutant induction of this gene was strongly reduced. The present study demonstrated that in addition to biochemical regulation of GgpS activity, alterations of ggpS expression are involved in regulation of GG synthesis in Synechocystis sp. strain PCC 6803. A model showing the interaction of the two regulatory levels is presented.The strategies used by bacteria to survive in environments with high and changing salinities have received much attention in the last few years. The general physiological response after an upshift of the salt concentration in a medium includes three phases. First, inorganic ions (usually Na ϩ and Cl Ϫ ) enter the cell after the turgor collapse resulting from the large difference in water potentials across the cytoplasmic membrane. Second, Na ϩ is exchanged for K ϩ , which saves the cell metabolism from the toxic influence of high Na ϩ concentrations. Stabilization of turgor by accumulation of ions as a long-term acclimation strategy is possible only in halophilic archaea and some halophilic bacteria. Therefore, in the third phase so-called compatible solutes are usually accumulated, which allows exclusion of the inorganic ions without a further change of turgor (1).For some model organisms, like the gram-negative enteric bacterium Escherichia coli, the gram-positive soil bacterium Bacillus subtilis, and the cyanobacterial freshwater isolate Synechocystis sp. strain PCC 6803, the acclimation processes have been investigated in detail. In minimal media these strains produce by de novo synthesis amounts of the compatible solutes trehalose (E. coli) (11), proline (B. subtilis) (26), and glucosylglycerol (GG) (Synechocystis) that are proportional to the stress (20,5). Mutants defective in trehalose, proline, or GG production exhib...

The SigB σ Factor Regulates Multiple Salt Acclimation Responses of the Cyanobacterium Synechocystis sp. PCC 6803

“…Many His kinases (Shoumskaya et al, 2005), three group 2 s factors SigB, SigC, and SigE (Pollari et al, 2008), two group 3 s factors (Huckauf et al, 2000;Marin et al, 2002), and a transcriptional repressor protein, GppR (Klähn et al, 2010) have been identified as potential regulators of salt acclimation of Synechocystis cells. Figure 9 summarizes salt acclimation processes that are at least partly regulated by the SigB factor.…”

“…Inactivation of the group 2 s factor SigB leads to a salt-sensitive phenotype, and also the DsigC and DsigE strains grow slowly after addition of 0.7 M NaCl (Pollari et al, 2008). Furthermore, inactivation of the group 3 s factor SigF delayed the activation of the ggps gene and the accumulation of glucosylglycerol (Marin et al, 2002). A specific repressor protein, GppR, that suppresses the expression of the ggpS gene under lowsalt conditions was recently discovered (Klähn et al, 2010).…”

“…In Synechocystis, as in many other moderately halotolerant species, the main compatible solute is glucosylglycerol (Hagemann, 2011). Salt addition activates an inactive form of glucosylglycerol-phosphate synthase, and also enhances the transcription of the ggpS gene encoding glucosylglycerol-phosphate synthase (Marin et al, 2002;Stirnberg et al, 2007;Hagemann, 2011;Novak et al, 2011). In the fourth phase, typically occurring 2 to 12 h after the onset of salt stress, compatible solutes accumulate to such high concentrations that they are mainly responsible for the maintenance of the osmotic potential.…”

Na+-dependent K+ Uptake Ktr System from the Cyanobacterium Synechocystis sp. PCC 6803 and Its Role in the Early Phases of Cell Adaptation to Hyperosmotic Shock

“…PCC 6803 and Synechocystis sp. PCC 6714 (15)(16)(17)(18)(19). The other indication of the involvement of the KtrB system in long term osmoadapatation (Fig.…”

“…kazusa.or.jp/cyano/). During its long term adaptation to high NaCl concentrations, this organism also synthesizes and accumulates glucosylgylcerol (17)(18)(19). Determining from the genome sequence, strain PCC 6803 has been predicted to contain at least three types of K ϩ uptake systems, Kdp system, which is probably of minor importance (20), a Ktr system (21), which appears to play a role in salt stress by high NaCl concentrations (20) and K ϩ channels.…”