Robert H, Le Marrec C, Blanco C, Jebbar M
Laboratoire de Microbiologie Alimentaire et Biotechnologie, ENSSTAB, Université Bordeaux I, 33405 Talence, France.
Appl Environ Microbiol. 2000 Feb;66(2):509-17. doi: 10.1128/AEM.66.2.509-517.2000.
Natural-abundance (13)C-nuclear magnetic resonance was used to probe the intracellular organic solute content of the moderately halophilic bacterium Tetragenococcus halophila. When grown in complex growth media supplemented or not with NaCl, T. halophila accumulates glycine betaine and carnitine. Unlike other moderate halophiles, T. halophila was not able to produce potent osmoprotectants (such as ectoines and glycine betaine) through de novo synthesis when cultured in defined medium under hyperosmotic constraint. Addition of 2 mM carnitine, glycine betaine, or choline to defined medium improved growth parameters, not only at high salinity (up to 2.5 M NaCl) but also in media lacking NaCl. These compounds were taken up when available in the surrounding medium. The transport activity occurred at low and high salinities and seems to be constitutive. Glycine betaine and carnitine were accumulated by T. halophila in an unmodified form, while exogenously provided choline led to an intracellular accumulation of glycine betaine. This is the first evidence of the existence of a choline-glycine betaine pathway in a lactic acid bacterium. An assay showed that the compatible solutes strikingly repressed the accumulation of glutamate and slightly increased the intracellular potassium level only at high salinity. Interestingly, osmoprotectant-treated cells were able to maintain the intracellular sodium concentration at a relatively constant level (200 to 300 nmol/mg [dry weight]), independent of the NaCl concentration of the medium. In contrast, in the absence of osmoprotectant, the intracellular sodium content increased sharply from 200 to 2,060 nmol/mg (dry weight) when the salinity of the medium was raised from 1 to 2 M. Indeed, the imported compatible solutes play an actual role in regulating the intracellular Na(+) content and confer a much higher salt tolerance to T. halophila.
利用天然丰度的(13)C-核磁共振技术探究嗜盐四联球菌这种中度嗜盐细菌的细胞内有机溶质含量。当嗜盐四联球菌在添加或不添加氯化钠的复杂生长培养基中生长时，会积累甘氨酸甜菜碱和肉碱。与其他中度嗜盐菌不同，当在高渗条件下的限定培养基中培养时，嗜盐四联球菌无法通过从头合成产生有效的渗透保护剂（如四氢嘧啶和甘氨酸甜菜碱）。向限定培养基中添加2 mM肉碱、甘氨酸甜菜碱或胆碱可改善生长参数，不仅在高盐度（高达2.5 M氯化钠）下如此，在缺乏氯化钠的培养基中也是如此。当周围培养基中有这些化合物时，它们会被摄取。转运活性在低盐度和高盐度下均会发生，且似乎是组成型的。嗜盐四联球菌以未修饰的形式积累甘氨酸甜菜碱和肉碱，而外源提供的胆碱会导致细胞内甘氨酸甜菜碱的积累。这是首次在乳酸菌中发现胆碱-甘氨酸甜菜碱途径存在的证据。一项分析表明，相容性溶质仅在高盐度下显著抑制谷氨酸的积累，并略微提高细胞内钾离子水平。有趣的是，经渗透保护剂处理的细胞能够将细胞内钠浓度维持在相对恒定的水平（200至300 nmol/mg[干重]），与培养基中的氯化钠浓度无关。相比之下，在没有渗透保护剂的情况下，当培养基盐度从1 M提高到2 M时，细胞内钠含量从200 nmol/mg急剧增加到2060 nmol/mg（干重）。实际上，导入的相容性溶质在调节细胞内Na(+)含量方面发挥着实际作用，并赋予嗜盐四联球菌更高的耐盐性。
