SGER: Investigation of Nannobacteria and Their Role in Mineral Precipitation

纳米细菌很小（一般为0.1微米，但直径在0.025-0.3微米之间），呈球形、卵形、棒状或球链状。它们最初是在对意大利维泰博温泉石灰华进行高倍扫描电镜研究时在岩石中发现的。石灰华中的小特征与“正常”细菌在形态上的相似性，以及它们倾向于以与细菌相同的方式聚集在菌落中，这使得Folk（1992）提出这些特征是“侏儒型”细菌。他进一步提出，由于阳离子被带负电荷的细胞壁吸引，它们通过创造有利于成核的微环境来促进沉淀（Folk, 1993a；另见Beveridge， 1989）。由于纳米细菌的直径约为“正常”细菌的十分之一（体积的1/1000）(“纳米细菌”一词最初是由微生物学家研究饥饿，因此小的细菌时使用的（Morita, 1988），它们的性质或起源是微生物学中一个重要的争议点。反对纳米细菌是自由生物体的主要论点是，它们太小，无法包含基因组（包括核糖体在内的生物合成能力）和细胞壁或细胞膜。然而，这一论点是基于以下可能不正确的假设：纳米细菌的DNA干重的比例将与已知的全尺寸细菌相当；纳米细菌的含水量与已知的营养生物相当；而且纳米细菌是自由生活的。关于纳米细菌性质的其他假设包括细菌寄生虫、细菌孢子/休眠阶段、细胞碎片周围的矿物沉淀或大有机分子周围的沉淀。实验表明，这些球状和椭球状的纹理不是金涂层、酸蚀刻、光束损伤的结果，也不是污染微量矿物质的结果（Folk和Lynch， 1997）。

9803031 George Nannobacteria are small (generally ~0.1 um, but ranging from 0.025-0.3um diameter) features that appear as spheres, ovoids, rods, or linked chains of balls. They were first discovered in rocks during high-magnification (50,000X) SEM study of Hot Springs travertine from Viterbo, Italy. The Morphologic similarity between the small features in the travertine and "normal" bacteria, and their tendency to occur clustered in colonies in the same manner as bacteria, lead Folk (1992) to propose that the features were "dwarf form" bacteria. He further suggested that they promoted precipitation by creating microenvironments conducive to nucleation due to cation attraction to a negatively charged cell wall (Folk, 1993a; see also Beveridge, 1989). Because nannobacteria are about one-tenth the diameter (1/1000 the volume) of "normal" bacteria (the term "nannobacteria" was first used by a microbiologist researching starved, therefore small, bacteria (Morita, 1988) their nature or origin is a point of significant microbiological controversy. The primary argument against nannobacteria being free living organisms is that they are too small to contain a genome (biosynthetic capacity including ribosomes), and a cell wall or membrane. This argument, however, is based on the following assumptions that may not be true: that the proportion of the nannobacterial dry weight that is DNA would be comparable to that of known full-size bacteria; that the water content of nannobacteria is comparable to that of known vegetative organisms; and that nannobacteria are free-living. Alternative hypotheses for the nature of nannobacteria include bacterial parasites, bacterial spores/resting stages, mineral precipitation around cell fragments, or precipitation around large organic molecules. Experimentation has shown that these ball-and ellipsoid-shaped textures are not the result of gold-coating, acid-etching, beam damage, nor are they contaminant trace minerals (Folk and Lynch, 1997).