Miller A G, Turpin D H, Canvin D T
J Bacteriol. 1984 Jul;159(1):100-6. doi: 10.1128/jb.159.1.100-106.1984.
We have found that Na+ is required for the alkalotolerance of the cyanobacterium Synechococcus leopoliensis. Cell division did not occur at any pH in the absence of Na+, but cells inoculated into Na+-free growth medium at pH 6.8 did continue metabolic activity, and over a period of 48 h, the cells became twice their normal size. Many of these cells remained viable for at least 59 h and formed colonies on Na+ -containing medium. Cells grown in the presence of Na+ and inoculated into Na+ -free growth medium at pH 9.6 rapidly lost viability. An Na+ concentration of ca. 0.5 milliequivalents X liter-1 was required for sustained growth above pH 9.0. The Na+ requirement could be only partially met by Li+ and not at all by K+ or Rb+. Cells incubated in darkness in growth medium at pH 6.8 had an intracellular pH near neutrality in the presence or absence of Na+. When the external pH was shifted to 9.6, only cells in the presence of Na+ were able to maintain an intracellular pH near 7.0. The membrane potential, however, remained high (-120 mV) in the absence or presence of Na+ unless collapsed by the addition of gramicidin. Thus, the inability to maintain a neutral intracellular pH at pH 9.6 in the absence of Na+ was not due to a generalized disruption of membrane integrity. Even cells containing Na+ still required added Na+ to restore photosynthetic rates to normal after the cells had been washed in Na+ -free buffer at pH 9.6. This requirement was only partially met by Li+ and was not met at all by K+, Rb+, Cs+ Mg2+, or Ca2+. The restoration of photosynthesis by added Na+ occurred within 30 s and suggests a role for extracellular Na+. Part of our results can be explained in terms of the operation of an Na+/H+ antiporter activity in the plasma membrane, but some results would seem to require other mechanisms for Na+ action.
我们发现，钠离子是嗜碱蓝藻聚球藻碱耐受性所必需的。在没有钠离子的情况下，细胞在任何pH值下都不发生分裂，但接种到pH 6.8的无钠生长培养基中的细胞确实继续进行代谢活动，并且在48小时内，细胞体积变为正常大小的两倍。这些细胞中的许多至少存活59小时，并在含钠培养基上形成菌落。在有钠离子存在的情况下生长并接种到pH 9.6的无钠生长培养基中的细胞迅速失去活力。在pH 9.0以上持续生长需要约0.5毫当量/升的钠离子浓度。锂离子只能部分满足对钠离子的需求，而钾离子、铷离子则完全不能满足。在pH 6.8的生长培养基中黑暗孵育的细胞，无论有无钠离子，细胞内pH值都接近中性。当外部pH值变为9.6时，只有在有钠离子存在的情况下细胞才能将细胞内pH值维持在7.0左右。然而，无论有无钠离子，膜电位都保持在较高水平（-120 mV），除非加入短杆菌肽使其崩溃。因此，在没有钠离子的情况下，无法在pH 9.6时维持中性细胞内pH值并非由于膜完整性的普遍破坏。即使含有钠离子的细胞在pH 9.6的无钠缓冲液中洗涤后，仍需要添加钠离子才能将光合速率恢复正常。锂离子只能部分满足这一需求，而钾离子、铷离子、铯离子、镁离子或钙离子则完全不能满足。添加钠离子后光合作用在30秒内恢复，这表明细胞外钠离子具有一定作用。我们的部分结果可以用质膜中钠氢反向转运体活性的运作来解释，但有些结果似乎需要钠离子作用的其他机制。
