Saum Stephan H, Müller Volker
Molecular Microbiology & Bioenergetics, Institute of Molecular Biosciences, Goethe University Frankfurt, Frankfurt am Main, Germany.
Saline Syst. 2008 Apr 28;4:4. doi: 10.1186/1746-1448-4-4.
The moderate halophile Halobacillus halophilus is the paradigm for chloride dependent growth in prokaryotes. Recent experiments shed light on the molecular basis of the chloride dependence that is reviewed here. In the presence of moderate salinities Halobacillus halophilus mainly accumulates glutamine and glutamate to adjust turgor. The transcription of glnA2 (encoding a glutamine synthetase) as well as the glutamine synthetase activity were identified as chloride dependent steps. Halobacillus halophilus switches its osmolyte strategy and produces proline as the main compatible solute at high salinities. Furthermore, Halobacillus halophilus also shifts its osmolyte strategy at the transition from the exponential to the stationary phase where proline is exchanged by ectoine. Glutamate was found as a "second messenger" essential for proline production. This observation leads to a new model of sensing salinity by sensing the physico-chemical properties of different anions.
嗜盐嗜碱芽孢杆菌是原核生物中依赖氯化物生长的典型代表。近期的实验揭示了此处所综述的氯化物依赖性的分子基础。在中等盐度条件下，嗜盐嗜碱芽孢杆菌主要积累谷氨酰胺和谷氨酸以调节膨压。glnA2（编码谷氨酰胺合成酶）的转录以及谷氨酰胺合成酶活性被确定为依赖氯化物的步骤。嗜盐嗜碱芽孢杆菌会改变其渗透调节物质策略，并在高盐度下产生脯氨酸作为主要的相容性溶质。此外，嗜盐嗜碱芽孢杆菌在从指数生长期向稳定期转变时也会改变其渗透调节物质策略，此时脯氨酸会被四氢嘧啶取代。谷氨酸被发现是脯氨酸产生所必需的“第二信使”。这一观察结果导致了一种通过感知不同阴离子的物理化学性质来感知盐度的新模型。
