Biophysical characterization of changes in amounts and activity of Escherichia coli cell and compartment water and turgor pressure in response to osmotic stress
Biophysical characterization of changes in amounts and activity of Escherichia coli cell and compartment water and turgor pressure in response to osmotic stress
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DOI：
10.1016/s0006-3495(00)76726-9
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发表时间：
2000-04-01
影响因子：
3.4
通讯作者：
Record, MT Jr
中科院分区：
文献类型：
--
作者：
Cayley, DS;Guttman, HJ;Record, MT Jr
为了获得膨压，细胞内渗透压，和细胞质水活性的大肠杆菌作为渗透压的生长的函数，我们已经定量和分析的细胞，细胞质和周质水的量作为渗透压的生长和渗透压的非生长细胞与NaCl的质膜的功能。影响是巨大的;在0.03 Osm下，在基本培养基中生长的细胞的NaCl（质体）滴定将细胞质和细胞水减少至其原始值的类似20%和类似50%，并将周质水增加至类似300%。对细胞质和细胞水量的独立分析表明，膨压随着生长的渗透压的增加而降低，从0.03 Osm时的近似3.1 atm降低到0.1 Osm时的近似1.5 atm，再降低到高于0.5 Osm时的小于0.5 atm。根据文献分析数据和测量的周质体积计算的周质膜衍生寡糖（MDO）浓度作为渗透压的函数的分析提供了膨压随渗透压增加而降低的独立证据，并验证了细胞质和周质渗透压相等。我们认为MDO在低至中等渗透压下对周质体积的调节起关键作用。在高生长渗透压下，只有少量的细胞质水被观察到，小膨压的E。大肠杆菌的细胞质水活度仅略低于细胞外水活度。从这些研究结果中，我们推断，细胞质水的活性超过其摩尔分数在高渗透压，因此，得出结论，细胞质水的活性系数随着增长的渗透压增加，并超过统一在高渗透压，大概是由于大分子拥挤。这些新的发现是有意义的热力学分析的影响，在生长渗透压的变化对生物聚合物的过程中一般和调节过程，特别是在E。coli细胞质。
To obtain turgor pressure, intracellular osmolalities, and cytoplasmic water activity of Escherichia coli as a function of osmolality of growth, we have quantified and analyzed amounts of cell, cytoplasmic, and periplasmic water as functions of osmolality of growth and osmolality of plasmolysis of nongrowing cells with NaCl. The effects are large; NaCl (plasmolysis) titrations of cells grown in minimal medium at 0.03 Osm reduce cytoplasmic and cell water to similar to 20% and similar to 50% of their original values, and increase periplasmic water by similar to 300%. independent analysis of amounts of cytoplasmic and cell water demonstrate that turgor pressure decreases with increasing osmolality of growth, from similar to 3.1 atm at 0.03 Osm to similar to 1.5 at 0.1 Osm and to less than 0.5 atm above 0.5 Osm. Analysis of periplasmic membrane-derived oligosaccharide (MDO) concentrations as a function of osmolality, calculated from literature analytical data and measured periplasmic volumes, provides independent evidence that turgor pressure decreases with increasing osmolality, and verifies that cytoplasmic and periplasmic osmolalities are equal. We propose that MDO play a key role in periplasmic volume regulation at tow-to-moderate osmolality. At high growth osmolalities, where only a small amount of cytoplasmic water is observed, the small turgor pressure of E. coli demonstrates that cytoplasmic water activity is only slightly less than extracellular water activity. From these findings, we deduce that the activity of cytoplasmic water exceeds its mole fraction at high osmolality, and, therefore, conclude that the activity coefficient of cytoplasmic water increases with increasing growth osmolality and exceeds unity at high osmolality, presumably as a consequence of macromolecular crowding. These novel findings are significant for thermodynamic analyses of effects of changes in growth osmolality on biopolymer processes in general and osmoregulatory processes in particular in the E. coli cytoplasm.