Holland Daryl P, Walsby Anthony E
School of Biological Sciences, University of Bristol, Bristol BS8 1UG, UK.
J Microbiol Methods. 2009 May;77(2):214-24. doi: 10.1016/j.mimet.2009.02.005. Epub 2009 Feb 20.
The gas vesicles of the cyanobacterium Microcystis sp. collapse under pressures ranging from 0.65-1.10 MPa, determined from turbidity changes in a pressure nephelometer. In turgid cells, collapse occurs at a lower range of pressures; the difference is equal to the cell turgor pressure. The turgor pressure decreases, however, as gas vesicles collapse; this decrease is minimised by calculating the turgor pressure in samples with few of their gas vesicles collapsed. Previously, pressure and turbidity were measured in discrete steps, using analogue meters, or continuously, using chart recorders: turgor pressure was calculated from the mean or median collapse pressures. We describe modifications allowing continuous digital recording; the output was modelled with polynomial or sigmoid functions, the latter providing the best fit over the full collapse-pressure curve; turgor pressure could then be calculated for any point on the collapse-pressure curve. The shape of the collapse-pressure curve was affected by the rate of pressure rise; curves were similar to those from step-wise methods when the pressure was raised at approximately 4 kPa s(-1). Under a rapid, almost instantaneous, rise in pressure there was a larger initial decrease in turgor and from the subsequent recovery the hydraulic conductivity of the cell surface could be calculated; the new method gave improved measurements of the cell volumetric elastic modulus. Following collapse of half the gas vesicles, cells recovered their full turgor pressure after 3 h. This suggests turgor homeostasis. These methods are applicable to other bacteria with gas vesicles, including Escherichia coli, if it could be genetically modified to express transgenic gas vesicles.
通过压力散射浊度计中浊度的变化测定，蓝藻微囊藻属的气体囊泡在0.65 - 1.10兆帕的压力下会塌陷。在膨胀的细胞中，塌陷发生在较低的压力范围内；差值等于细胞膨压。然而，随着气体囊泡塌陷，膨压会降低；通过计算气体囊泡很少塌陷的样品中的膨压，这种降低可降至最低。以前，压力和浊度是使用模拟仪表以离散步骤测量的，或者使用图表记录仪连续测量：膨压是根据平均或中值塌陷压力计算得出的。我们描述了允许连续数字记录的改进方法；输出结果用多项式或S形函数建模，后者在整个塌陷压力曲线上拟合效果最佳；然后可以计算塌陷压力曲线上任何一点的膨压。塌陷压力曲线的形状受压力上升速率的影响；当压力以约4千帕秒⁻¹的速度上升时，曲线与逐步测量方法得到的曲线相似。在压力快速、几乎瞬间上升的情况下，膨压最初会有较大下降，从随后的恢复情况可以计算细胞表面的水力传导率；新方法改进了细胞体积弹性模量的测量。一半的气体囊泡塌陷后，细胞在3小时后恢复了其全部膨压。这表明存在膨压稳态。这些方法适用于其他具有气体囊泡的细菌，包括大肠杆菌，如果它可以通过基因改造来表达转基因气体囊泡的话。
