Germination and Amplification of Anthrax Spores by Soil-Dwelling Amoebas
Germination and Amplification of Anthrax Spores by Soil-Dwelling Amoebas
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DOI：
10.1128/aem.02034-12
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发表时间：
2012-11-01
影响因子：
4.4
通讯作者：
Glomski, Ian J.
中科院分区：
文献类型：
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作者：
Dey, Rafik;Hoffman, Paul S.;Glomski, Ian J.
虽然炭疽通常与生物恐怖主义有关，但在世界许多地方，炭疽杆菌（Bacillus anthracis）在土壤中流行，导致牲畜散发疾病。这些土壤通常富含有机物和钙，可促进有弹性的炭疽芽孢杆菌孢子的存活。炭疽病的爆发往往发生在降雨后的温暖天气，据信降雨会使孢子集中在径流聚集的低洼地区。得出的结论是，孢子浓度升高并不是营养生长的结果，因为炭疽芽孢杆菌与本土细菌的竞争能力较差。在这里，我们测试了另一种假设，其中常见于潮湿土壤和死水池中的变形虫通过促进发芽和细胞内繁殖而充当炭疽芽孢杆菌孢子的放大器。在模拟环境条件下，我们发现炭疽杆菌在卡氏棘阿米巴内发芽和繁殖。以孢子形式接种的全毒力炭疽芽孢杆菌 Ames 菌株（含有 pX01 和 pX02 毒力质粒）和疫苗菌株 Sterne（仅含有 pX01）与卡斯氏曲霉共培养的生长动力学显示，72 小时后孢子数量增加了近 50 倍。相反，无质粒菌株9131几乎没有生长，这表明质粒pX01对于A.castellanii的生长至关重要。电子和延时荧光显微镜显示，孢子在变形虫吞噬体内萌发，营养杆菌进行增殖，并且在变形虫死亡后，杆菌在细胞外环境中形成孢子。该分析支持我们的假设，即阿米巴原虫有助于炭疽杆菌在自然环境中的持久存在和扩增。
While anthrax is typically associated with bioterrorism, in many parts of the world the anthrax bacillus (Bacillus anthracis) is endemic in soils, where it causes sporadic disease in livestock. These soils are typically rich in organic matter and calcium that promote survival of resilient B. anthracis spores. Outbreaks of anthrax tend to occur in warm weather following rains that are believed to concentrate spores in low-lying areas where runoff collects. It has been concluded that elevated spore concentrations are not the result of vegetative growth as B. anthracis competes poorly against indigenous bacteria. Here, we test an alternative hypothesis in which amoebas, common in moist soils and pools of standing water, serve as amplifiers of B. anthracis spores by enabling germination and intracellular multiplication. Under simulated environmental conditions, we show that B. anthracis germinates and multiplies within Acanthamoeba castellanii. The growth kinetics of a fully virulent B. anthracis Ames strain (containing both the pX01 and pX02 virulence plasmids) and vaccine strain Sterne (containing only pX01) inoculated as spores in coculture with A. castellanii showed a nearly 50-fold increase in spore numbers after 72 h. In contrast, the plasmidless strain 9131 showed little growth, demonstrating that plasmid pX01 is essential for growth within A. castellanii. Electron and time-lapse fluorescence microscopy revealed that spores germinate within amoebal phagosomes, vegetative bacilli undergo multiplication, and, following demise of the amoebas, bacilli sporulate in the extracellular milieu. This analysis supports our hypothesis that amoebas contribute to the persistence and amplification of B. anthracis in natural environments.