A highly effecient and universal solid medium for growing mesophilic and moderately thermophilic, iron-oxidizing, acidophilic bacteria

Abstract

A solid medium is described which has proved highly successful and reproducible in growing all strains (>50) of Thiobacillus ferrooxidans, Leptospirillum ferrooxidans and moderately thermophilic iron-oxidizing bacteria that have thus far been tested. Its preparation involves incorporating an acidophilic heterotroph in a ferrous iron/tryptone soya broth medium, and covering the set gel with a layer of sterile medium. Comparisons are made of the suitability of different heterotrophs for this purpose. Pre-adapting heterotrophic bacteria to the environment of the solid medium (in particular the iron concentration) was found to improve both the plate efficiencies and the growth rates of iron-oxidizing acidophiles. The incorporation of a heterotroph reduced the concentration of monosaccharides, though not total soluble carbohydrate, in solid media. Differences in colony sizes and morphologies on overlay plates enabled T. ferrooxidans and L. ferrooxidans to be differentiated in mixed populations.