Carrera M, Zandomeni R O, Sagripanti J-L
Research & Technology Directorate, Edgewood Chemical Biological Center, U.S. Army Aberdeen Proving Ground, Maryland, USA.
J Appl Microbiol. 2008 Jul;105(1):68-77. doi: 10.1111/j.1365-2672.2008.03758.x. Epub 2008 Feb 20.
To determine the wet and dry density of spores of Bacillus anthracis and compare these values with the densities of other Bacillus species grown and sporulated under similar conditions.
We prepared and studied spores from several Bacillus species, including four virulent and three attenuated strains of B. anthracis, two Bacillus species commonly used to simulate B. anthracis (Bacillus atrophaeus and Bacillus subtilis) and four close neighbours (Bacillus cereus, Bacillus megaterium, Bacillus thuringiensis and Bacillus stearothermophilus), using identical media, protocols and instruments. We determined the wet densities of all spores by measuring their buoyant density in gradients of Percoll and their dry density in gradients of two organic solvents, one of high and the other of low chemical density. The wet density of different strains of B. anthracis fell into two different groups. One group comprised strains of B. anthracis producing spores with densities between 1.162 and 1.165 g ml(-1) and the other group included strains whose spores showed higher density values between 1.174 and 1.186 g ml(-1). Both Bacillus atrophaeus and B. subtilis were denser than all the B. anthracis spores studied. Interestingly and in spite of the significant differences in wet density, the dry densities of all spore species and strains were similar. In addition, we correlated the spore density with spore volume derived from measurements made by electron microscopy analysis. There was a strong correlation (R(2) = 0.95) between density and volume for the spores of all strains and species studied.
The data presented here indicate that the two commonly used simulants of B. anthracis, B. atrophaeus and B. subtilis were considerably denser and smaller than all B. anthracis spores studied and hence, these simulants could behave aerodynamically different than B. anthracis. Bacillus thuringiensis had spore density and volume within the range observed for the various strains of B. anthracis. The clear correlation between wet density and volume of the B. anthracis spores suggest that mass differences among spore strains may be because of different amounts of water contained within wet dormant spores.
Spores of nonvirulent Bacillus species are often used as simulants in the development and testing of countermeasures for biodefense against B. anthracis. The similarities and difference in density and volume that we found should assist in the selection of simulants that better resemble properties of B. anthracis and, thus more accurately represent the performance of countermeasures against this threat agent where spore density, size, volume, mass or related properties are relevant.
测定炭疽芽孢杆菌孢子的湿密度和干密度，并将这些值与在相似条件下生长和形成芽孢的其他芽孢杆菌属的密度进行比较。
我们使用相同的培养基、方案和仪器，制备并研究了几种芽孢杆菌属的孢子，包括4株强毒株和3株减毒株炭疽芽孢杆菌、2种常用于模拟炭疽芽孢杆菌的芽孢杆菌属（萎缩芽孢杆菌和枯草芽孢杆菌）以及4种近缘菌（蜡样芽孢杆菌、巨大芽孢杆菌、苏云金芽孢杆菌和嗜热脂肪芽孢杆菌）。我们通过测量其在Percoll梯度中的浮力密度以及在两种化学密度一高一低的有机溶剂梯度中的干密度，来测定所有孢子的湿密度。不同株炭疽芽孢杆菌的湿密度分为两个不同的组。一组包括产生密度在1.162至1.165 g/ml之间孢子的炭疽芽孢杆菌株，另一组包括其孢子显示更高密度值在1.174至1.186 g/ml之间的菌株。萎缩芽孢杆菌和枯草芽孢杆菌都比所研究的所有炭疽芽孢杆菌孢子密度更大。有趣的是，尽管湿密度存在显著差异，但所有孢子种类和菌株的干密度相似。此外，我们将孢子密度与通过电子显微镜分析测量得出的孢子体积相关联。在所研究的所有菌株和种类的孢子中，密度与体积之间存在很强的相关性（R² = 0.95）。
此处呈现的数据表明，两种常用于模拟炭疽芽孢杆菌的菌株，萎缩芽孢杆菌和枯草芽孢杆菌，比所研究的所有炭疽芽孢杆菌孢子密度大得多且体积小得多，因此，这些模拟菌株在空气动力学方面的表现可能与炭疽芽孢杆菌不同。苏云金芽孢杆菌的孢子密度和体积在所观察到的各种炭疽芽孢杆菌菌株范围内。炭疽芽孢杆菌孢子湿密度与体积之间的明显相关性表明，孢子菌株之间的质量差异可能是由于湿休眠孢子中所含水量不同。
无毒芽孢杆菌属的孢子常用于开发和测试针对炭疽芽孢杆菌生物防御对策的模拟物。我们发现的密度和体积的异同应有助于选择更类似于炭疽芽孢杆菌特性的模拟物，从而在孢子密度、大小、体积、质量或相关特性相关时，更准确地代表针对这种威胁病原体的对策性能。
