title: Comparative analysis of kdp and ktr mutants reveals distinct roles of the potassium transporters in the model cyanobacterium Synechocystis sp. strain PCC 6803.
abstract: 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 on-chip 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(+) concentration under conditions of limited K(+) in natural environments, whereas Ktr mediates fast potassium movements in the presence of greater K(+) availability. Through their distinct activities, both Ktr and Kdp coordinate the responses of Synechocystis to changes in K(+) levels under fluctuating environmental conditions.
authors.affiliation: Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Sendai, Japan.
authors.forename: Kei
authors.initials: K
authors.lastname: Nanatani
authors.affiliation: Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Sendai, Japan.
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Shijuku
authors.affiliation: Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Sendai, Japan.
authors.forename: Yousuke
authors.initials: Y
authors.lastname: Takano
authors.affiliation: Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Sendai, Japan.
authors.forename: Lalu
authors.initials: L
authors.lastname: Zulkifli
authors.affiliation: School of Agricultural Sciences, Nagoya University, Nagoya, Japan.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Yamazaki
authors.affiliation: Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Sendai, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Tominaga
authors.affiliation: Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Sendai, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Souma
authors.affiliation: Center for Gene Research, Nagoya University, Nagoya, Japan.
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Onai
authors.affiliation: Center for Gene Research, Nagoya University, Nagoya, Japan.
authors.forename: Megumi
authors.initials: M
authors.lastname: Morishita
authors.affiliation: Center for Gene Research, Nagoya University, Nagoya, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Ishiura
authors.affiliation: Department of Plant Physiology, University of Rostock, Rostock, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Hagemann
authors.affiliation: Faculty of Life and Environmental Sciences, University of Tsukuba, Ibaraki, Japan.
authors.forename: Iwane
authors.initials: I
authors.lastname: Suzuki
authors.affiliation: Department of Micro-Nano Systems Engineering, Graduate School of Engineering, Nagoya University, Nagoya, Japan.
authors.forename: Hisataka
authors.initials: H
authors.lastname: Maruyama
authors.affiliation: Department of Micro-Nano Systems Engineering, Graduate School of Engineering, Nagoya University, Nagoya, Japan.
authors.forename: Fumihito
authors.initials: F
authors.lastname: Arai
authors.affiliation: Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Sendai, Japan uozumi@biophy.che.tohoku.ac.jp.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Uozumi
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D001692:Biological Transport; D027682:Cation Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D009876:Operon; D011188:Potassium / Q000378:metabolism; D046939:Synechocystis / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D027682:Cation Transport Proteins; D011188:Potassium