Laboratory for Core Technology, Development Kirin Beverage Co, Ltd,, Technovillage 3F, 1-17-1 Namamugi, Yokohama 230-8628, Japan.
J Nanobiotechnology. 2012 Jun 7;10:22. doi: 10.1186/1477-3155-10-22.
Despite the availability of conventional devices for making single-cell manipulations, determining the hardness of a single cell remains difficult. Here, we consider the cell to be a linear elastic body and apply Young's modulus (modulus of elasticity), which is defined as the ratio of the repulsive force (stress) in response to the applied strain. In this new method, a scanning probe microscope (SPM) is operated with a cantilever in the "contact-and-push" mode, and the cantilever is applied to the cell surface over a set distance (applied strain).
We determined the hardness of the following bacterial cells: Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and five Bacillus spp. In log phase, these strains had a similar Young's modulus, but Bacillus spp. spores were significantly harder than the corresponding vegetative cells. There was a positive, linear correlation between the hardness of bacterial spores and heat or ultraviolet (UV) resistance.
Using this technique, the hardness of a single vegetative bacterial cell or spore could be determined based on Young's modulus. As an application of this technique, we demonstrated that the hardness of individual bacterial spores was directly proportional to heat and UV resistance, which are the conventional measures of physical durability. This technique allows the rapid and direct determination of spore durability and provides a valuable and innovative method for the evaluation of physical properties in the field of microbiology.
尽管有常规的单细胞操作设备，但要确定单个细胞的硬度仍然很困难。在这里，我们将细胞视为线性弹性体，并应用杨氏模量（弹性模量），其定义为响应施加应变的斥力（应力）与施加应变的比值。在这种新方法中，扫描探针显微镜（SPM）以“接触-推动”模式操作悬臂，并将悬臂施加到细胞表面一段设定的距离（施加应变）。
我们确定了以下细菌细胞的硬度：大肠杆菌、金黄色葡萄球菌、铜绿假单胞菌和五种芽孢杆菌。在对数生长期，这些菌株具有相似的杨氏模量，但芽孢杆菌孢子比相应的营养细胞硬得多。细菌孢子的硬度与耐热性或耐紫外线（UV）性之间存在正线性相关性。
使用该技术，可以根据杨氏模量确定单个营养细菌细胞或孢子的硬度。作为该技术的应用，我们证明了单个细菌孢子的硬度与耐热性和耐紫外线（UV）性直接成正比，这是物理耐久性的常规衡量标准。该技术允许快速直接地确定孢子的耐久性，并为微生物学领域的物理特性评估提供了一种有价值的创新方法。
