Two Types of Morphologically Distinct Fibers Comprising Gallionella ferruginea Twisted Stalks

摘要

Bacteria belonging to the genus Gallionella produce uniquely twisted extracellular stalks and are ubiquitous inhabitants of ocherous deposits that form in freshwater bodies (2). This genus has had an anfractuous history of nomenclature, as described in detail by Silva (7), but the current genus name has gained acceptance by most researchers (2). Although several names for this species have been proposed since the beginning of the 19 th century, the term Gallionella ferruginea has been commonly used for the most ubiquitous species found worldwide. Despite some past and present debates, it seems conceivable that the genus may consist of only a single species (G. ferruginea) and all the other described species are only ecological variants of it (5); however, much of the detailed taxonomical position of this genus is still obscure because of the lack of isolated strains. S?gaard et al. (8) used microscopy to compare iron (Fe) sludge from filter systems belonging to three different Danish freshwater plants and found that the stalks of G. ferruginea collected from one plant were composed of small, twisted parallel threads, whereas those from the other two plants were larger and typically twisted, suggesting that the two types of stalks might belong to different species. Several papers (2, 4, 6, 8, 10) have reported the ultrastructure of G. ferruginea cells and their associated stalks but the structural and elemental associations of the cells and stalks are still not well understood.