Ten strains of extremely acidophilic bacteria, isolated from different environments form a distinct monophyletic clade within the phylum Firmicutes. Comparison of complete genomes of the proposed type strains confirm that they comprise two genera (proposed names Sulfoacidibacillus and Ferroacidibacillus), and at least three species (Sulfoacidibacillus ferrooxidans, Sulfoacidibacillus thermotolerans and Ferroacidibacillus organovorans). The bacterial strains share some physiological traits, including catalysing the dissimilatory oxidation and reduction of iron, and in being obligately heterotrophic. Both species of Sulfoacidibacillus are also able to oxidise elemental sulfur and tetrathionate. Both S. ferrooxidans and Ferroacidibacillus spp. are mesophilic, while S. thermotolerans isolates are moderate thermophiles. The isolates display different degrees of acid-tolerance: Ferroacidibacillus spp. are the most acid-sensitive while the type strain of S. ferrooxidans grows at pH 0.9. MK7 was detected as the sole menaquinone present in all three nominated type strains, and their peptidoglycans all contain meso-2,6 diaminopimelic acid type A1γ. The chromosomal DNA of the strains examined contain between 44 and 52 mol% G + C. The nominated type strains of the new species are S. ferrooxidans S0ABT (= DSM 105355T = JCM 33225T); S. thermotolerans Y002T (= ATCC TSD-104T = JCM 31946T); F. organovorans SLC66T (= ATCC TSD-103T = JCM 31945T).
Keywords: Acidophiles; Ferroacidibacillus; Iron oxidation; Oxidation; Sulfoacidibacillus.
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