Energetic problems of extremely alkaliphilic aerobes
Energetic problems of extremely alkaliphilic aerobes
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DOI：
10.1016/0005-2728(96)00044-8
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发表时间：
1996-07-18
影响因子：
4.3
通讯作者：
Hicks, DB
中科院分区：
文献类型：
--
作者：
Krulwich, TA;Ito, M;Hicks, DB
对极端嗜碱芽孢杆菌属物种的十多年的研究已经阐明了这些细菌在pH值远远超过10的生长期间调节其细胞质pH的非凡能力。然而，各种有趣的充满活力的问题有关的Na+依赖的pH值稳态机制尚未得到解决。它们包括：（1）澄清细胞表面层如何在嗜碱菌中发挥作用，这是这种情况;（2）鉴定推定的产电Na+/H+反向转运蛋白，在至少一些嗜碱菌中，其可以完全解释比外部pH低2个pH单位以上的细胞质pH;（3）确定特定的模块或辅助蛋白质是否对这种反向转运蛋白的功效是必需的;（4）在高的外部pH值下跨膜电位增加的机制基础，在该pH值下，消耗反向转运蛋白必须是最活跃的;（5）解释了极端嗜碱杆菌中pH稳态的Na+特异性，而至少在一些非嗜碱需氧菌中，K+对pH稳态的几乎等同的功效。将概述亲碱能量学这一中心领域此类研究的现状和未来策略。还考虑，将是策略，以阐明强大的H+耦合氧化磷酸化的基础上，嗜碱菌在pH值超过10。维持细胞质pH值低于高外部pH值2个单位以上，导致体积电化学质子梯度（Δ p）较低。为了绕过这种低Δ p，Na+偶联用于溶质吸收，即使是来自不是特别富含Na+的环境的嗜中温性嗜碱菌。这表明这些细菌确实经历了低Δ p，这种偶联是一种适应。可能的原因和机制，使用H+耦合，而不是Na+耦合ATP合酶在这种情况下将进行讨论。
Over a decade of work on extremely alkaliphilic Bacillus species has clarified the extraordinary capacity that these bacteria have for regulating their cytoplasmic pH during growth at pH values well over 10. However, a variety of interesting energetic problems related to their Na+-dependent pH homeostatic mechanism are yet to be solved. They include: (1) the clarification of how cell surface layers play a role in a category of alkaliphiles for which this is the case; (2) identification of the putative, electrogenic Na+/H+ antiporter(s) that, in at least some alkaliphiles, may completely account for a cytoplasmic pH that is over 2 pH units lower than the external pH; (3) the determination of whether specific modules or accessory proteins are essential for the efficacy of such antiporters; (4) the mechanistic basis for the increase in the transmembrane electrical potential at the high external pH values at which the potential-consuming antiporter(s) must be most active; and (5) an explanation for the Na+-specificity of pH homeostasis in the extremely alkaliphilic bacilli as opposed to the almost equivalent efficacy of K+ for pH homeostasis in at least some non-alkaliphilic aerobes. The current status of such studies and future strategies will be outlined for this central area of alkaliphile energetics. Also considered, will be strategies to elucidate the basis for robust H+-coupled oxidative phosphorylation by alkaliphiles at pH values over 10. The maintenance of a cytoplasmic pH over 2 units below the high external pH results in a low bulk electrochemical proton gradient (Delta p). To bypass this low Delta p, Na+-coupling is used for solute uptake even by alkaliphiles that are mesophiles from environments that are not especially Na+-rich. This indicates that these bacteria indeed experience a low Delta p, to which such coupling is an adaptation. Possible reasons and mechanisms for using a H+-coupled rather than a Na+-coupled ATP synthase under such circumstances will be discussed.