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).
