Electron Transport Systems of the Chemoautotroph Ferrobacillus Ferrooxidans. I. Cytochrome C-containing Iron Oxidase.

Ferrobacillus ferrooxidans was isolated and named by Leathen and Braley (1) in 1954 and reported to be an obligate chemoautotroph which utilizes the oxidation of inorganic ferrous iron as a primary energy source. A somewhat similar bacterium, called Thiobaeillus ferrooxiduns, had previously been isolated by Cohner, Temple, and Hinkle (2) and characterized as an obligate chemoautotroph which would grow on either ferrous iron or thiosulfate. The taxonomic position of F. ferrooxidans was questioned recently by Unz and Lundgren (3) on the basis of a nutritional study of F. ferrooxidans, T. ferrooxidans, and an unnamed iron-oxidizing bacterium, isolated from Utah mine water, which closely resembled a chemoautotroph previously isolated from the same source by Beck (4). The growth of all three bacteria was supported by an inorganic medium containing either ferrous iron, elemental sulfur, or thiosulfate as the sole energy source, although the generation time varied with the energy source and the bacterium. Unz and Lundgren, therefore, suggested that F. ferrooxtians be identified as a strain of T. ferrooxidans and the genus Ferrobacillus be abolished. The classification of F. ferrooxidans, the above mentioned isolate of Beck (4), reported to grow on ferrous iron or sulfur and possibly on thiosulfate, and of a similar bacterium called Ferrobacillus sulfooxiduns, isolated by Kinsel (5) and reported to grow on either ferrous iron or sulfur, must therefore be considered to be tentative at this time. Studies of the physiology and biochemistry of F. ferrooxidans, as in the case of other iron-oxidizing chemoautotrophs, have been somewhat limited, owing in part to the difficulty of obtaining large numbers of cells in pure culture. The recent development by Silverman and Lundgren (6) of a method for the growth of F. ferrooxidum which gives appreciable yields, usually between 1 and 2 g of cells (wet weight) per 18 liters of media, now makes possible more extensive investigations of this organism. Manometric studies by the same authors (7) of intact cells during iron oxidation demonstrated that the oxygen uptake was 92% or more of the theoretical uptake predicted by the equation