title: Novel insights into the role of potassium for osmoregulation in Halomonas elongata.
abstract: The role of K(+) in osmoregulation of the halophilic bacterium Halomonas elongata was investigated. At lower salinities (0.51 M NaCl), K(+) was the predominant cytoplasmic solute (1.25 micro mol mg protein(-1)). At higher salinities (1.03 M NaCl) ectoine became the main cytoplasmic solute (1.57 micro mol mg protein(-1)), while the K(+) content remained unchanged. In response to osmotic upshock, cells of H. elongata simultaneously accumulated ectoine and K(+) glutamate. The ectoine and K(+) glutamate levels in osmotically stressed cells exceeded the level of cells adapted to high salinities. The increase in K(+) glutamate was long lasting (>120 min) and not transient, as described for non-halophiles. Regulation of the synthesis of ectoine and glutamate was proven to occur mainly at the level of enzyme activity. Limitation of K(+) inhibited the growth of salt-adapted H. elongata cells, especially at high salinities, and caused a decrease of the intracellular organic solute content, inhibition of respiration, and an abolition of the cell's ability to respond to osmotic stress. The saturation constant K(S) for K(+) was estimated to be 105 micro M at a salinity of 0.51 M NaCl, indicating that an uptake system of medium affinity is responsible for K(+) accumulation in H. elongata.
authors.affiliation: Institut für Mikrobiologie und Biotechnologie, Rheinische Friedrich-Wilhelms Universität, Meckenheimer Allee 168, 53115 Bonn, Germany.
authors.forename: Annette
authors.initials: A
authors.lastname: Kraegeloh
authors.forename: Hans Jörg
authors.initials: HJ
authors.lastname: Kunte
mesh_terms: D000222:Adaptation, Physiological; D000599:Amino Acids, Diamino / Q000096:biosynthesis; D020632:Halomonas / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D017136:Ion Transport; D009997:Osmotic Pressure; D010101:Oxygen Consumption; D011188:Potassium / Q000494:pharmacology / Q000502:physiology*; D012462:Saline Solution, Hypertonic / Q000494:pharmacology; D014882:Water-Electrolyte Balance / Q000502:physiology*
chemical_list: D000599:Amino Acids, Diamino; D012462:Saline Solution, Hypertonic; C045628:ectoine; D011188:Potassium