The Genus Siderocapsa (and Other Iron- and Manganese-Oxidizing Eubacteria)

Abstract

This chapter discusses those species of Siderocapsa and members of the family Siderocapsaceae (Pribram, 1929) whose morphology, ecology, and, to some extent, culture physiology have been so exactly described that, in spite of disagreement concerning their taxonomic position, there can be no doubt of their existence and great ecological significance. The discussion concentrates on such existing and ecologically significant representatives of this family in order to preserve the practical orientation of this Handbook. Information on many genera and species whose position is uncertain has been drawn together in Bergey’s Manual of Determinative Bacteriology, eighth edition (Buchanan and Gibbons, 1974; contributor G. A. Zavarzin) and seventh edition (Breed et al., 1957; contributor R. S. Breed in cooperation with H. Beger) and by Dorff (1934). A comparison of the genera and species treated in these references provides a bird’s-eye view of this entire group of organisms. The family Siderocapsaceae is defined as unicellular, nonfilamentous or nonstalkforming, iron and/or manganese bacteria that are able to deposit these metal oxides under natural conditions, on or in capsules or on extracellular mucoid material excreted by these bacteria. This definition is taxonomically rather imperfect, but for practical purposes it is quite adequate. That the validity of this family, in particular of the species of the genus Siderocapsa, has often been questioned is to be ascribed exclusively to the present taxonomic inadequacy of the definition. Such questions have been raised most recently by Dubinina and Zhdanov (1975); but a final clarification of the taxonomic question will not be possible until the complete developmental cycle of these bacteria in their natural habitat has been clearly described. Culture experiments are doubtless very helpful here, but they cannot provide a final clarification of the taxonomic question as long as the natural development of the organisms remains unknown. Merely because there have been controversial questions of taxonomy it does not follow that these bacteria do not exist. Their existence and great ecological significance have become firmly established in the last decades through the discovery of their mass development in the hypolimnion of many lakes.