Kraegeloh Annette, Kunte Hans Jörg
Institut für Mikrobiologie und Biotechnologie, Rheinische Friedrich-Wilhelms Universität, Meckenheimer Allee 168, 53115 Bonn, Germany.
Extremophiles. 2002 Dec;6(6):453-62. doi: 10.1007/s00792-002-0277-4. Epub 2002 Jul 13.
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.
研究了钾离子在嗜盐细菌长枝盐单胞菌渗透调节中的作用。在较低盐度（0.51M NaCl）下，钾离子是主要的细胞质溶质（1.25微摩尔/毫克蛋白质）。在较高盐度（1.03M NaCl）下，四氢嘧啶成为主要的细胞质溶质（1.57微摩尔/毫克蛋白质），而钾离子含量保持不变。响应渗透压升高，长枝盐单胞菌细胞同时积累四氢嘧啶和钾离子-谷氨酸。渗透胁迫细胞中的四氢嘧啶和钾离子-谷氨酸水平超过了适应高盐度的细胞水平。钾离子-谷氨酸的增加是持久的（>120分钟），而不是像非嗜盐菌那样是短暂的。已证明四氢嘧啶和谷氨酸的合成调节主要发生在酶活性水平。钾离子限制抑制了适应盐环境的长枝盐单胞菌细胞的生长，尤其是在高盐度下，并导致细胞内有机溶质含量降低、呼吸抑制以及细胞对渗透胁迫反应能力的丧失。在0.51M NaCl盐度下，钾离子的饱和常数K(S)估计为105微摩尔，这表明中等亲和力的摄取系统负责长枝盐单胞菌中钾离子的积累。
