Glaser D, Haines M, Bylund J, Higgins M
Department of Microbiology and Immunology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140.
J Bacteriol. 1989 Sep;171(9):4992-5. doi: 10.1128/jb.171.9.4992-4995.1989.
The buoyant density of whole cells of Streptococcus faecium varies with growth rate and during the cell cycle. Two possible explanations for this were explored: (i) the density of cell walls may vary, and (ii) the proportions of wall and cytoplasm may vary. We tested the first possibility by isolating walls from chilled, unfixed populations of S. faecium cells and fractionating them on Percoll density gradients. Mean cell wall density averaged 4% less than whole-cell density and did not vary significantly with growth rate. In addition, walls isolated from heavy and light fractions of a population of cells did not differ significantly in density. Thus, variation in the density of isolated cell walls could not account for the observed variation in whole-cell density within or between populations. Using previously published measurements of the physical dimensions of S. faecium cells, we also found that the relative proportions of wall and cytoplasm (see the second possibility above) could not account for the observed changes in whole-cell buoyant density.
粪肠球菌全细胞的浮力密度随生长速率和细胞周期而变化。对此有两种可能的解释：（i）细胞壁的密度可能不同，（ii）细胞壁和细胞质的比例可能不同。我们通过从冷却、未固定的粪肠球菌细胞群体中分离细胞壁，并在Percoll密度梯度上对其进行分级分离，来检验第一种可能性。平均细胞壁密度比全细胞密度平均低4%，且不随生长速率显著变化。此外，从细胞群体的重馏分和轻馏分中分离出的细胞壁在密度上没有显著差异。因此，分离出的细胞壁密度的变化不能解释在群体内部或群体之间观察到的全细胞密度的变化。利用先前发表的粪肠球菌细胞物理尺寸的测量数据，我们还发现细胞壁和细胞质的相对比例（见上述第二种可能性）不能解释观察到的全细胞浮力密度的变化。
