STUDIES ON THE CHEMOAUTOTROPHIC IRON BACTERIUM FERROBACILLUS FERROOXIDANS

Studies of the biochemistry and physiology of the obligate chemolithoautotrophs have been largely restricted to the genus Thiobaciilus (Vishniac and Santer, 1957) and the nitrifying bacteria (Fry and Peel, 1954; Lees, 1955; Engel and Alexander, 1958). Such studies were made possible by the prior development of media and methods that would yield large numbers of physiologically active cells. Unfortunately, parallel developments with the obligate autotrophic iron bacteria have not proceeded at similar rates. Interest in the iron bacteria has remained high ever since Winogradsky first postulated that the energy derived from the oxidation of ferrous iron could serve as the sole support for the growth of a C02-assimilating microorganism. Since then, a variety of species of iron bacteria has been described in the literature, where it appears that the only requisite for this appellation is the ability to precipitate oxidized iron in sheaths, stalks, capsules, or the surrounding medium. But, it is doubtful whether iron oxidation by most of these organisms contributes materially to the energy supply needed for growth, i. e., they are heterotrophs (Pringsheim, 1949a, b; Stokes, 1954). To our knowledge, only a few species are presently considered to be obligate chemoautotrophs; namely Gallionella spp., Thiobacillus ferrooxidans, and Ferrobacillus ferrooxidans. The recent work of Kucera and Wolfe (1957) with Gallionella ferruginea has demonstrated the difficulty of obtaining suitable yields of this organism in pure culture. Further, their photographs indicate that separation of cells from the tangled mass of inert stalks would indeed be a formidable task. The