The Genus Gallionella

Abstract

The bacteria of the genus Gallionella belong to the so-called “iron bacteria,” which achieved their theoretical importance after Winogradsky (1888, 1922) postulated his conception of chemolithotrophy for these organisms. These bacteria also have practical significance since they clog drains, water pipes, and wells with deposits of iron oxide compounds. In connection with freshwater supply problems and the rapid growth of agriculture, hydrotechnicians and land-reclamation (underground drainage) specialists have become increasingly interested in bacterial iron oxidation as a common source of interference with wells and drainage systems (Ford, 1978; Hanert, 1974b; Khrutskaya, 1970; Martin et al., 1978). Iron bacteria are also interesting for ecological and biogeochemical reasons. Like algae, iron bacteria may develop in their natural habitats in such masses that the idea of their participation in the sedimentary formation of iron ore is plausible, as was recognized in the first description of the iron bacterium Gallionella ferruginea (Ehrenberg, 1836). Iron bacteria are reputed to be difficult to work with. The general opinion of microbiologists is that it is difficult to cultivate these organisms in the laboratory and that there are difficulties in isolating and identifying them. Therefore, it is one of the main purposes of this contribution to show that this poor reputation is unjustified. It will be demonstrated that cultivation and handling of the treated bacteria are in no way more difficult than for other microorganisms, if attention is paid to only a few fundamental peculiarities, such as “sessility” and “gradient growth.” Disregard of these factors may be one of the most common practical reasons for failure to locate these organisms in natural habitats, for failure to cultivate them successfully, for misinterpretation of presumed developmental stages, and for discouragement which can often be observed when students are starting in this field. Therefore, the following text is narrowly restricted to methods and practical advice—without any theoretical discussion on the controversial life cycle, taxonomic position, and physiology, which are described in the literature cited.