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. Differences among the strains were evident in cell size (4.2 by 0.6 to 1.2 by 0.6 p.m), 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-plus-cytosine base composition of eight typical strains ranged from 63 to 68 mol%. All of the strains exhibited primary characteristics of the recently described genus however, important differences between our strains and the type species suggested that new species should be described. No significant deoxyribonucleic acid-deoxyribonucleic acid homology was found between five acidophilic heterotrophic strains and Furthermore, no significant deoxyribonucleic acid-deoxyribonucleic acid homology was evident between the acidophilic heterotrophs and six 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: (type strain, strain OP [= ATCC 35905]), (type strain, strain KLB [= ATCC 35903]), and (type strain, strain PW2 [= ATCC 35904]).


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