Comparative Analysis of kdp and ktr Mutants Reveals Distinct Roles of the Potassium Transporters in the Model Cyanobacterium Synechocystis sp. Strain PCC 6803

Abstract

f Photoautotrophic bacteria have developed mechanisms to maintain K ؉ homeostasis under conditions of changing ionic concentrations in the environment. Synechocystis sp. strain PCC 6803 contains genes encoding a well-characterized Ktr-type K ؉ uptake transporter (Ktr) and a putative ATP-dependent transporter specific for K ؉ (Kdp). The contributions of each of these K ؉ transport systems to cellular K ؉ homeostasis have not yet been defined conclusively. To verify the functionality of Kdp, kdp genes were expressed in Escherichia coli, where Kdp conferred K ؉ uptake, albeit with lower rates than were conferred by Ktr. An onchip microfluidic device enabled monitoring of the biphasic initial volume recovery of single Synechocystis cells after hyperosmotic shock. Here, Ktr functioned as the primary K ؉ uptake system during the first recovery phase, whereas Kdp did not contribute significantly. The expression of the kdp operon in Synechocystis was induced by extracellular K ؉ depletion. Correspondingly, Kdp-mediated K ؉ uptake supported Synechocystis cell growth with trace amounts of external potassium. This induction of kdp expression depended on two adjacent genes, hik20 and rre19, encoding a putative two-component system. The circadian expression of kdp and ktr peaked at subjective dawn, which may support the acquisition of K ؉ required for the regular diurnal photosynthetic metabolism. These results indicate that Kdp contributes to the maintenance of a basal intracellular K Living cells have developed specific responses to hyperosmotic shock. Upon exposure to this stress, cells initially lose water and their volume shrinks. In all living cells, K ϩ is the major intracellular cation used for the maintenance of turgor pressure, cytosolic osmolarity, protein structuring, and membrane potential (1-3). In contrast to animals, Na ϩ /K ϩ ATP pumps are generally missing in bacteria and plants. Hence, these cells possess K ϩ uptake transporters to supply K ϩ to the cells. Particularly after hyperosmotic stress, cells quickly take up K ϩ from the medium to increase the intracellular osmolarity, which prevents water efflux from the cell. Data from genetic and biochemical experiments indicate that the activity and the expression of these transporters respond to hyperosmotic stress. In the later phase of acclimation to hyperosmotic stress, cells also induce the synthesis of osmoprotective molecules, such as glutamate, trehalose, proline, and glucosylglycerol (4, 5). Despite an increasing amount of data on cellular osmoregulation involving ion flux across the membrane, direct evidence for the involvement of specific transporters in the cellular response to osmotic up-shock is lacking for photoautotrophic organisms.The cyanobacterium Synechocystis sp. strain PCC 6803 (hereinafter referred to as Synechocystis) is a frequently used unicellular photosynthetic prokaryote that can survive under a wide range of environmental conditions (6). Unlike Escherichia coli, Synechocystis possesses an internal thylakoid membrane system, which...

Current knowledge and recent advances in understanding metabolism of the model cyanobacteriumSynechocystissp. PCC 6803

“…Synechocystis encodes two PM localized potassium (K + ) uptake systems, Ktr (KtrA/KtrB) and Kdp (KdpA, KdpB, KdpC, KdpD) [217]. The Ktr system mediates rapid K + uptake while the Kdp system maintains K + levels under limiting conditions in the environment [217,218]. KtrC was initially incorrectly assigned as a subunit of the Ktr complex [219], but was later assigned to monoglucosyldiacylglycerol synthesis, not K + import [134].…”

Reduction of Spermidine Content Resulting from Inactivation of Two Arginine Decarboxylases Increases Biofilm Formation in Synechocystis sp. Strain PCC 6803

“…The intensity of stress, the physiological state of the cells, and polyamine synthesis may form a more complicated interrelationship in Synechocystis, influencing its lifestyle. ligated into the AflII-NdeI sites of pNS1::lacZϩCm r d (6). Using the resultant plasmid, Padc1::lacZ or Padc2::lacZ was integrated into the TS1 region in the Synechocystis genome.…”

“…Disruption mutations of adc1 (slr1312) and adc2 (slr0662) were generated by insertion of a kanamycin resistance gene into adc1 and a spectinomycin resistance gene into adc2, respectively (Fig. 5A) (6). The mutant strains ko1, kd2, and ko1ko2 were then selected by successive streaking to homogeneity segregation in BG11 medium containing kanamycin (20 g/ml) and/or spectinomycin (20 g/ml) at 29°C.…”

“…strain PCC 6803 is a unicellular photosynthetic prokaryote that can survive a wide range of environmental conditions and therefore can be used as a model for the study of molecular response mechanisms to various stresses (4). Several membrane transport systems in Synechocystis function in the maintenance of intracellular ion homeostasis (5,6). Prolonged exposure to a high-salinity environment induces morphological changes as well as the production of extracellular components.…”

Mechanical characterization system of cyanobacteria using a robot integrated microdluidic chip

“…Mechanosensitive channels response to increasing intracellular pressure for decreasing intracellular pressure. Previously, this osmotic adaptation mechanism was evaluated from the observation of the cellular size taken from images [7]. Since ion channels may response to intracellular pressure, we investigate the cellular mechanical characteristics such as stiffness.…”