Vreeland R H, Rosenzweig W D, Powers D W
Department of Biology, West Chester University, Pennsylvania 19383, USA.
Nature. 2000 Oct 19;407(6806):897-900. doi: 10.1038/35038060.
Bacteria have been found associated with a variety of ancient samples, however few studies are generally accepted due to questions about sample quality and contamination. When Cano and Borucki isolated a strain of Bacillus sphaericus from an extinct bee trapped in 25-30 million-year-old amber, careful sample selection and stringent sterilization techniques were the keys to acceptance. Here we report the isolation and growth of a previously unrecognized spore-forming bacterium (Bacillus species, designated 2-9-3) from a brine inclusion within a 250 million-year-old salt crystal from the Permian Salado Formation. Complete gene sequences of the 16S ribosomal DNA show that the organism is part of the lineage of Bacillus marismortui and Virgibacillus pantothenticus. Delicate crystal structures and sedimentary features indicate the salt has not recrystallized since formation. Samples were rejected if brine inclusions showed physical signs of possible contamination. Surfaces of salt crystal samples were sterilized with strong alkali and acid before extracting brines from inclusions. Sterilization procedures reduce the probability of contamination to less than 1 in 10(9).
已发现细菌与多种古代样本有关联，然而由于样本质量和污染问题，很少有研究被普遍接受。当卡诺和博鲁茨基从被困在2500万至3000万年前琥珀中的一只灭绝蜜蜂体内分离出一株球形芽孢杆菌时，仔细的样本选择和严格的灭菌技术是研究被认可的关键。在此，我们报告了从二叠纪萨拉多组形成的一块2.5亿年前盐晶体中的盐水包裹体中分离并培养出一种此前未被识别的形成芽孢的细菌（芽孢杆菌属，命名为2-9-3）。16S核糖体DNA的完整基因序列表明，该生物体是死海芽孢杆菌和泛栖盐芽孢杆菌谱系的一部分。精细的晶体结构和沉积特征表明，自形成以来盐并未重新结晶。如果盐水包裹体有可能被污染的物理迹象，则样本会被拒收。在从包裹体中提取盐水之前，先用强碱和强酸对盐晶体样本的表面进行灭菌。灭菌程序将污染概率降低至小于十亿分之一。
