SGER: Investigation of Nannobacteria and Their Role in Mineral Precipitation

乔治9803031 纳米细菌是小的（通常约0.1 μ m，但直径范围为0.025- 0.3 μ m）特征，其表现为球体、卵形体、杆或球的链接链。 在对意大利维泰博的温泉石进行高倍率（50，000倍）扫描电镜研究时，首次在岩石中发现了它们。 由于细菌和“正常”细菌的小特征在形态上的相似性，以及它们以与细菌相同的方式聚集在菌落中的倾向，Folk（1992）提出这些特征是“侏儒型”细菌。 他进一步提出，由于阳离子吸引到带负电荷的细胞壁，它们通过创造有利于成核的微环境来促进沉淀（Folk，1993 a;也参见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）（术语“纳米细菌”首先由研究饥饿的微生物学家使用，因此细菌很小（Morita，1988）），它们的性质或起源是一个重要的微生物学争议点。 反对纳米细菌是自由生物体的主要论点是它们太小而不能包含基因组（包括核糖体的生物合成能力）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：纳米细菌干重中DNA的比例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;以及纳米细菌是自由生活的。 纳米细菌的性质的替代假设包括细菌寄生虫，细菌孢子/休眠期，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，这些球形和椭圆形的纹理不是金涂层、酸蚀刻、束损伤的结果，也不是污染的微量矿物质（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).