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The Genera Leptothrix and Sphaerotilus

Introduction

Representatives of the genera Leptothrix and Sphaerotilus were among the first microorganisms to be recognized in the environment and described in detail by scientists. The type species of the genus Leptothrix, L. ochracea, was already observed in the late eighteenth century and described by Roth (1797) under the synonym "Conferva ochracea." Later, Kützing (1843) proposed to place this species within the genus Leptothrix. Ten years earlier, the same author had published a description of the species Sphaerotilus natans (Kützing, 1833), which is today still known under this name. These early publications were probably evoked by the observation of ocherous deposits (clearly visible to the naked eye) in ponds or slowly running water. A microscopic examination of these suspicious aggregates led then to the discovery of filamentous microorganisms, which were obviously responsible for the deposition of iron or ferromanganese oxides in a slimy