Water relations in single cells.
Water relations in single cells.
复制标题
单细胞中的水关系。
DOI：
10.1098/rstb.1977.0035
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发表时间：
1977
期刊：
影响因子：
--
通讯作者：
J. C. Measures
中科院分区：
文献类型：
--
作者：
G. Gould;J. C. Measures
细胞内水分含量是影响微生物单细胞在不利环境条件下生长和存活的重要因素。某些类型的细菌、酵母、丝状真菌和藻类能够在水分活度低于0.9甚至低至0.6的环境中生长，是已知的渗透耐受性最强的生物体。决定这种极端渗透压耐受性的两个最重要的因素是：（1）细胞中的酶对存在的溶质的抵抗力，以及（2）细胞在其自身内维持特定溶质的能力，这些溶质与细胞内酶的持续活性相容，处于足以平衡外部渗透压的水平，从而避免脱水。这种相容性溶质的水平是通过代谢控制的，包括酵母中的多元醇、渗透压耐受性最低的细菌中的谷氨酸、渗透压耐受性较高的细菌中的γ-氨基丁酸和脯氨酸以及特定嗜盐细菌中的钾。相反，在某些条件下，微生物中的渗透调节机制可能会减少而不是维持细胞的水含量。例如，在一些细菌形成内生孢子的形态发生变化过程中，会发生一种特殊形式的渗透调节，其中孢子外部区域新合成的负电性聚合物（“肽聚糖”）引起并维持（而不是避免）中央核心的脱水。事实上，孢子的耐热性可以通过渗透操作通过实验进行可预测的改变。核心脱水机制可能与内生孢子的巨大耐热性有关。它还可能与此类细胞的特殊休眠和长寿有关，并提出了一种可能在其他休眠生物系统中发挥作用的原理。
The intracellular water content is an important factor affecting the growth and survival of single cells of microorganisms under adverse environmental conditions. Certain types of bacteria, yeasts, filamentous fungi and algae are capable of growth in environments with water activities below 0.9 and even as low as 0.6, and are the most osmotolerant living organisms known. The two most important factors that determine such extreme osmotolerance are: (1) the resistance of the enzymes in a cell to the solutes present, and (2) the cell’s ability to maintain within itself particular solutes, which are compatible with continued activity of intracellular enzymes, at levels sufficient to balance the external osmotic pressure and thus avoid dehydration. The levels of such compatible solutes are metabolically controlled and include polyols in yeasts, glutamic acid in the least osmotolerant bacteria, y-aminobutyric acid and proline in the more osmotolerant bacteria and potassium in specifically halophilic bacteria. In contrast, under certain conditions osmoregulatory mechanisms in microorganisms may reduce rather than maintain the water content of the cell. For example, during the morphogenic changes that accompany the formation of endospores by some bacteria, a special form of osmoregulation occurs in which a newly synthesized electronegative polymer (‘peptidoglycan’) in the outer region of the spore brings about and maintains, rather than avoids, dehydration of the central core. Indeed, spore heat resistance can be predictably modified experimentally by osmotic manipulation. The core dehydration mechanism is probably implicated in the enormous resistance of endospores to heat. It may also be involved in the exceptional dormancy and longevity of such cells, and suggests a principle that may operate in other dormant biological systems.