Bacterial cells were penetrated with chrysotile fibers and transformed to antibiotics resistance by incorporation of exogenous plasmid DNA

将静止相的受体大肠杆菌细胞、温石棉和pUC18供体DNA的悬浮液用条纹条多次铺展在LB琼脂平板上，导致大肠杆菌细胞内摄取质粒DNA。当细胞在温石棉中暴露60秒以上，琼脂浓度为2%时，转化效率最高。为了提高温石棉介导法的转化效率，我们对各种条件和参数进行了系统的优化。与不含阳离子的温石棉接触相比，接触阳离子可产生高达100倍的转化子。优化条件可使每μg pUC18DNA转化10^6个转化子。当细胞暴露在温石棉中时，由于琼脂平板表面的快速干燥而产生的剧烈物理变化，对于温石棉中介转化是必不可少的。我们认为，温石棉介导的DNA摄取是大肠杆菌机械物理转化的结果，因为大肠杆菌细胞在化学上不能胜任。暴露在温石棉中的细胞的电子显微镜显示，温石棉纤维穿透了大肠杆菌的膜。结果表明，质粒DNA转化大肠杆菌是由于温石棉纤维与其结合或吸附的结果。

A suspension of recipient E.coli cells in stationary phase, chrysotile asbestos, and pUC18 donor DNA was spread over the surface of an LB agar plate using a streak bar several times, resulted in intracellular uptake of the plasmid DNA by the E.coli cells. The transformation efficiency was highest with a duration of cell exposure to chrysotile for more than 60 seconds and a 2% agar concentration. To improve transformation efficiency by chrysotile mediation, we systematically optimized various conditions and parameters. In comparison to chrysotile exposure without cations, exposure with cations produced up to 100-fold more transformants. Optimized conditions resulted in 10^6 transformants per μg pUC18 DNA. The drastic physical change due to ‘quick drying on the surface of the agar plate', when cells were exposed to chrysotile, was essential for transformation by chrysotile mediation. We suggest that DNA uptake by chrysotile asbestos mediation is the result of a mechanical physical transformation of the E.coli, since E.coli cells are not competent chemically. Electron microscopy of cells exposed to chrysotile suggested penetration of the E.coli membrane by chrysotile fibers. It is suggested that E.coli transformation by the plasmid DNA was the result of penetration by chrysotile fibers to which plasmid DNA is bound or adsorbed.