Alicyclobacillus curvatus sp. nov. and Alicyclobacillus mengziensis sp. nov., two acidophilic bacteria isolated from acid mine drainage

Two acidophilic strains, designated as ALEF1(T) and S30H14(T), were isolated from acid mine drainage sediment. Cells of both strains were Gram-stain-positive, aerobic, endospore-forming rods. Strains ALEF1(T) and S30H14(T) were acidophilic and mesophilic, the former grew at 20–40 °C (optimum, 30 °C) and pH 2.5–4.5 (optimum, pH 3.5), while the latter grew at 20–45 °C (optimum, 30 °C) and pH 2.0–5.5 (optimum, pH 4.5). The 16S rRNA gene-based sequence analysis revealed that strains ALEF1(T) and S30H14(T) belonged to the genus Alicyclobacillus , and were phylogenetically close to Alicyclobacillus ferrooxydans TC-34(T) with 97.1 and 97.4% similarity, respectively. The similarity between the two novel strains was 98.6 %. The average nucleotide identity value between the genome sequences of ALEF1(T) and S30H14(T) was 79.5 %, and that between each of the two isolates and A. ferrooxydans TC-34(T) were 72.0 and 74.3 %. In addition, the digital DNA–DNA hybridization value between ALEF1(T) and S30H14(T) was 24.9 %, between strain ALEF1(T) and A. ferrooxydans TC-34(T) was 21.7 %, and between S30H14(T) and A. ferrooxydans TC-34(T) was 26.3 %, far below the interspecies threshold. Both strains could utilize diverse carbon sources for heterotrophic growth; strain ALEF1(T) could utilize ferrous iron as the energy source for autotrophic growth. Menaquinone 7 was the only quinone detected in either strain. Both strains contained anteiso-C(15 : 0) and anteiso-C(17 : 0), while ω-alicyclic fatty acids were not detected. Based on their phylogenetic positions, as well as phenotypic and genomic data, it is considered that strains ALEF1(T) and S30H14(T) represent two novel species within the genus Alicyclobacillus , for which the names Alicyclobacillus curvatus sp. nov. (type strain ALEF1(T)=CGMCC 1.17055(T)=KCTC 43124(T)) and Alicyclobacillus mengziensis sp. nov. (S30H14(T)=CGMCC 1.17050(T)=KCTC 43125(T)) are proposed.