The oxidation of Fe(2+) with oxygen in sulfate solutions was studied in the presence of T. ferrooxidans. To measure the chemical activity of bacteria, and the oxidation rate of iron, the redox potentials of solutions were continuously monitored during the experiments. The redox potentials were simultaneously monitored on the platinum and pyrite indicator electrodes. The redox potential versus time curves were further used to calculate the basic kinetic parameters, such as the reaction orders, the activation energy, and the frequency factor. It was found that under atmospheric conditions, and at Fe(2+) < 0.001M, T < 25 degrees C, and at pH above 2.2, the oxidation of iron is governed by the following rate expression: -(d[Fe(2+)]) / dt = 1.62 x 10(11)C(bact) [H(+)] [Fe(2+)] p O(2)e(-(58.77/RT)). Below pH = 2.2, the oxidation rate is independent of H(+) Concentration.

Acidophilic heterotrophic bacteria recovered from samples of water and sediment collected from acidic mine drainage streams were compared nutritionally, genetically, and morphologically. All 37 bacterial strains examined were rod shaped, motile, gram negative, and strictly aerobic, utilized citric acid and Tween 80 as sole carbon sources, and were unable to grow at or above pH 6.0. The ultrastructure of representative strains was not markedly different from that of gram-negative bacteria. Diverences among the strains were evident in cell size (4.2 by 0.6 to 1.2 by 0.6 pm), pigmentation (when present), and nutritional faculties (the carbon sources suitable for growth of individual strains ranged from 8 to 20 of the 32 compounds tested). The guanine-pluscytosine base composition of eight typical strains ranged from 63 to 68 mol%. All of the strains exhibited primary characteristics of the recently described genus Acidiphilium; however, important differences between our strains and the type species Acidiphilium cryptum suggested that new Acidiphilium species should be described. No significant deoxyribonucleic acid-deoxyribonucleic acid homology was found between five acidophilic heterotrophic strains and A. cryptum. Furthermore, no significant deoxyribonucleic aciddeoxyribonucleic acid homology was evident between the acidophilic heterotrophs and six Thiobacillus species. The bacteria which we studied could be divided into three groups based on genetic and nutritional characteristics. We propose the following three new species: Acidiphilium rubrum (type strain, strain OP [ = ATCC 35905]), Acidiphilium angustum (type strain, strain KLB [ = ATCC 35903]), and Acidiphilium facilis (type strain, strain PW2 [ = ATCC 359041).

Samples collected from Kesterson Reservoir were screened for bacterial presence and selenate reduction capability. Selenate concentrations of 100 mg/liter were not toxic to indigenous bacteria. Of the 44 samples collected, 20 possessed microbial populations capable of reducing selenate. Reduction was observed in 4% of the water samples, 92% of the sediment samples, and 100% of the soil samples. Microbial reduction of 100 mg of selenate per liter was complete within 1 week of incubation. Up to 75 mg of selenate per liter was reduced beyond selenite to an insoluble red precipitate. Data collected indicate that indigenous bacteria have a significant role in the biogeochemical cycling of selenium.

No abstract

Obligately acidophilic, heterotrophic bacteria were isolated both from enrichment cultures developed with acidic mine water and from natural mine drainage. The bacteria were grouped by the ability to utilize a number of organic acids as sole carbon sources. None of the strains were capable of chemolithotrophic growth on inorganic reduced iron and sulfur compounds. All bacteria were rod shaped, gram negative, nonencapsulated, motile, capable of growth at pH 2.6 but not at pH 6.0, catalase and oxidase positive, strictly aerobic, and capable of growth on citric acid. The bacteria were cultivatable on solid nutrient media only if agarose was employed as the hardening agent. Bacterial densities in natural mine waters ranged from approximately 20 to 250 cells per ml, depending upon source and culture medium. Ferric hydrates and stream vegetation contained from 1,500 to over 7 x 106 cells per g.