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Twelve isolates of thermophilic, acidophilic, cellulolytic bacteria were obtained from three different primary enrichment cultures from acidic hot springs at Yellowstone National Park, Wyo. The three isolates which had the highest cellulolytic activity, as shown by the diameter of clearing zones surrounding colonies on cellulose agar plates, were selected for intensive study. All were gram-variable, nonsporulating aerobic rods which formed no pigment. They grew at 37 to 65°C, with optimum growth at 55°C. The pH range for growth was 3.5 to 7, with an optimum pH of 5. The guanine-plus-cytosine content of the deoxyribonucleic acid was 60.7 ± 0.6 mol%. The organisms are resistant to penicillin G at 100 μg/ml. They share several important features with Thermus strains, namely heterotrophic, aerobic, and thermophilic mode of growth; morphological features; sensitivity to lysozyme; and presence of catalase. They differ in other important aspects, such as the pattern of carbon sources utilized for growth, the pH and temperature profiles of growth, the pattern of sensitivity to antibiotics, the guanine-plus-cytosine content of DNA, the composition of amino acids in the cell walls, and the structure of the cell walls. Thermus species are very sensitive to penicillin G, whereas our strains are resistant. Our strains also are different, in important respects, from the genus Thermomicrobium. Therefore, we designate the organism Acidothermus cellulolyticus gen. nov., sp. nov., of which the type strain is our strain 11B, ATCC 43068.
Mohagheghi et al. (Tue,) studied this question.