Böckelmann Uta, Lünsdorf Heinrich, Szewzyk Ulrich
Department of Environmental Microbiology, Technical University Berlin, Franklin Str. 29, 10587 Berlin, Germany.
Environ Microbiol. 2007 Sep;9(9):2137-44. doi: 10.1111/j.1462-2920.2007.01325.x.
Strain F8, a bacterial isolate from 'river snow', was found to produce extracellular fibres in the form of a filamentous network. These extracellular filaments, which were previously shown to be composed of DNA, have been studied for the first time by ultrastructural and electron energy-loss spectroscopy in the present work. 'Whole mount' preparations of strain F8 indicate these polymers are ultrastructurally homogeneous and form a network of elemental filaments, which have a width of 1.8-2.0 nm. When incubated at pH 3.5 with colloidal cationic ThO(2) tracers they become intensely stained (electron dense), affording direct evidence that the fibres are negatively charged and thus acidic chemically. Elemental analysis of the extracellular filaments by Energy-filtered Transmission Electron Microscopy revealed phosphorus to be the main element present and, because pretreatment of F8 cells with DNase prevented thorium labelling, the fibres must be composed of extracellular DNA (eDNA). Neither ultrathin sections nor 'whole mount negative stain' caused DNA release by general cell lysis. Additionally, cells infected with phages were never observed in ultrathin sections and phage particles were never detected in whole mount samples, which rules out the possibility of phages being directly involved in eDNA release.
菌株F8是从“河雪”中分离出的一种细菌，被发现能产生丝状网络形式的细胞外纤维。这些细胞外纤维先前已证明由DNA组成，在本研究中首次通过超微结构和电子能量损失光谱进行了研究。菌株F8的“整装”制剂表明，这些聚合物在超微结构上是均匀的，并形成了宽度为1.8 - 2.0纳米的基本细丝网络。当在pH 3.5下与胶体阳离子二氧化钍示踪剂一起孵育时，它们会被强烈染色（电子致密），这直接证明了这些纤维带负电荷，因此在化学上呈酸性。通过能量过滤透射电子显微镜对细胞外纤维进行元素分析，发现磷是主要存在元素，并且由于用DNA酶预处理F8细胞可阻止钍标记，所以这些纤维必定由细胞外DNA（eDNA）组成。超薄切片和“整装负染”均未通过一般细胞裂解导致DNA释放。此外，在超薄切片中从未观察到感染噬菌体的细胞，在整装样品中也从未检测到噬菌体颗粒，这排除了噬菌体直接参与eDNA释放的可能性。
