Group of bacteria found widely in nature in slow-running water. Many species are attached to underwater surfaces. They are characterized by a threadlike, branching arrangement of cells enclosed in a sheath. The sheaths of some are variously encrusted with iron or manganese oxides, depending on the water. One of the best-known is a common species, Sphaerotilus natans; in polluted water it has thin, colourless sheaths, and in unpolluted water containing iron it has yellow-brown, iron-encrusted sheaths that often grow into long slimy tassels.
This entry comes from Encyclopædia Britannica Concise.
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