STUDIES ON THE FILAMENTOUS SHEATHED IRON BACTERIUM SPHAEROTILUS NATANS

The extensive literature on the iron bacteria and the present status of our knowledge of this interesting group of microorganisms recently have been reviewed critically and exhaustively by Pringsheim (1949a). It is clear from this review that every aspect of the iron bacteriaecology, isolation, culture, morphology, nutrition, biochemistry, and taxonomy-requires extensive investigation if there is to be a sound knowledge of these microorganisms. The present investigations were begun as part of a systematic attempt to fill in some of the. existing gaps. The studies which are reported here are concerned with one of the commonest of the iron bacteria, Sphaerotilu natans. This orgaimsm was described and named first by Kttsing (1833) who noted its presence in large numbers in polluted waters. It was rediscovered later by Cohn (1875) under similar conditions, but because the filaments appeared to be dichotomously branched, although falsely so, Cohn thought that he had found a new organism and accordingly named it Cladothrix dichotoma. Both names have appeared in the subsequent literature and were considered by some investigators (Linde, 1913) to apply to one and the same organism and by others (Zikes, 1915) to organisms that are different. But Pringsheim (1949b) has shown that S. natans exhibits dichotomous false branching whenever it is grown in media of low organic matter content. It seems best, therefore, to consider C. dichotoma as being the cladothrix form of S. natans. In this paper, therefore, we shall use the name S. natans exclusively. Zopf (1882) claimed that S. natans is highly pleomorphic and described the occurrence of micrococci, vibrios, spirilla, and spirochetes along with the usual rod shaped cells. But this was based on observations of impure cultures and has not been supported by subsequent studies with pure strains. Biisgen (1894) was the