Kubitschek H E
Crit Rev Microbiol. 1987;14(1):73-97. doi: 10.3109/10408418709104436.
The behavior of cell buoyant density during the cell cycle has been determined for a number of different cell types, including bacteria, yeast, and mammalian cells. Mean buoyant density was extremely constant and independent of cell age during the cell cycle of the bacterium Escherichia coli, the fission yeast Schizosaccharomyces cerevisiae, the protozoan Amoebae proteus, cells from suspension cell cultures of mouse lymphoma and myeloma, and Chinese hamster ovary cells. In all of these cases, the buoyant densities of these cells were very narrowly distributed, with coefficients of variation of 0.1 to 0.3%. In contrast, buoyant density was variable in cells with thick cell walls and high buoyant densities. Density varied markedly during the cell cycle of the budding yeast Schizosaccharomyces cerevisiae and of the bacterium Streptococcus faecium. The average buoyant densities of cells in exponentially growing cultures of E. coli or Schizosaccharomyces pombe were also independent of growth rate of the cultures. Experiments with E. coli have established that cell buoyant density is controlled by the osmoregulatory system. Although the regulatory mechanisms for this control are unknown, the results suggest that the same or similar mechanisms regulate buoyant density in all of the cells that do not have unduly heavy cell walls and, therefore, these regulatory mechanisms were either conserved during evolution or reflect the convergent evolution found for organic osmolytes.
已针对多种不同类型的细胞测定了细胞周期中细胞浮力密度的行为，这些细胞类型包括细菌、酵母和哺乳动物细胞。在大肠杆菌、裂殖酵母、变形虫、小鼠淋巴瘤和骨髓瘤悬浮细胞培养物中的细胞以及中国仓鼠卵巢细胞的细胞周期中，平均浮力密度极其恒定，且与细胞年龄无关。在所有这些情况下，这些细胞的浮力密度分布非常狭窄，变异系数为0.1%至0.3%。相比之下，具有厚细胞壁和高浮力密度的细胞中浮力密度是可变的。在芽殖酵母和粪链球菌的细胞周期中，密度有明显变化。大肠杆菌或粟酒裂殖酵母指数生长培养物中细胞的平均浮力密度也与培养物的生长速率无关。对大肠杆菌的实验已证实细胞浮力密度受渗透调节系统控制。尽管这种控制的调节机制尚不清楚，但结果表明，在所有没有过厚细胞壁的细胞中，相同或相似的机制调节浮力密度，因此，这些调节机制要么在进化过程中得以保留，要么反映了有机渗透物的趋同进化。
