Strain S30A2^T, isolated from the acid mine drainage sediment of Mengzi Copper Mine, Yunnan, is proposed to represent a novel species of the sulphur-oxidizing genus Acidithiobacillus. Cells were Gram-stain-negative, non-endospore forming, highly motile with one or two monopolar flagella and rod-shaped. The strain was mesophilic, growing at 30–50 °C (optimum, 38 °C), acidophilic, growing at pH 2.0–4.5 (optimum, pH 2.5), and tolerant of 0–4 % (w/v; 684 mol l⁻¹) NaCl. The 16S rRNA gene-based sequence analysis showed that strain S30A2^T belongs to the genus Acidithiobacillus and shows the largest similarity of 96.6 % to the type strain Acidithiobacillus caldus KU^T. The genomic DNA G+C content of strain S30A2^T was 59.25 mol%. The average nucleotide identity ANIb and ANIm values between strain S30A2^T and A. caldus KU^T were 70.95 and 89.78 %, respectively and the digital DNA–DNA hybridization value was 24.9 %. Strain S30A2^T was strictly aerobic and could utilize elementary sulphur and tetrathionate to support chemolithotrophic growth. The major cellular fatty acid of S30A2^T was C_19 : 1ω7c. The respiratory quinones were ubiquinone-8 and ubiquinone-7. Based upon its phylogenetic, genetic, phenotypic, physiologic and chemotaxonomic characteristics, strain S30A2^T is considered to represent a novel species of the genus Acidithiobacillus, for which the name Acidithiobacillus acidisediminis sp. nov. is proposed. The type strain is S30A2^T (=CGMCC 1.17059^T=KCTC 72580^T).

A novel acidophilic, aerobic bacterium strain, MYW30-H2^T, was isolated from a heap of polymetallic mine. Cells of strain MYW30-H2^T were Gram-stain-positive, endospore-forming, motile, and rod-shaped. Strain MYW30-H2^T grew at a temperature range of 30–45 °C (optimum 40 °C) and a pH range of 3.5–6.0 (optimum 4.0) in the presence of 0–0.5% (w/v) NaCl. Strain MYW30-H2^T could grow heterotrophically on yeast extract and glucose, and grow mixotrophically using ferrous iron as an electron donor with yeast extract. Menaquinone-7 (MK-7) was the sole respiratory quinone of the strain. Iso-C_15:0 and anteiso-C_15:0 were the major cellular fatty acids. The 16S rRNA gene sequence analysis showed that MYW30-H2^T was phylogenetically affiliated with the family Alicyclobacillaceae, and the sequence similarity with other Alicyclobacillaceae genera species was below 91.51%. The average amino acid identity value of the strain with its phylogenetically related species was 52.3–62.1%, which fell into the genus boundary range. The DNA G+C content of the strain was 44.2%. Based on physiological and phylogenetic analyses, strain MYW30-H2^T represents a novel species of a new genus of the family Alicyclobacillaceae, for which the name Fodinisporobacter ferrooxydans gen. nov., sp. nov. is proposed. The type strain is MYW30-H2^T (=CGMCC 1.17422^T = KCTC 43278^T).

Tetrathionate hydrolase (TTH) is a key enzyme for the oxidation of reduced inorganic sulfur compounds (RISCs) with the S₄I pathway, which is distributed in autotrophic or facultative autotrophic sulfur-oxidizing bacteria and archaea. In this study, the enzyme TTH_Mc from the acidothermophilic archaeon Metallosphaera cuprina Ar-4^T, encoded by mcup_1281 and belonging to the pyrroloquinoline quinone (PQQ) family, has been shown to possess tetrathionate hydrolysis activity. The molecular mass of the single subunit of TTH_Mc was determined to be 57 kDa. TTH_Mc is proved to be located in the cytoplasm, periplasmic space, and membrane, and the activity of them accounted for 72.3%, 24.0%, and 3.7% of the total activity. Optimal activity was observed at temperatures above 95 °C and pH 6.0, and the kinetic constants K_m and V_max were 0.35 mmol/L and 86.3 μmol/L, respectively. The presence of 0.01 mol/L Mg²⁺ enhances the activity of TTH_Mc, while 0.01 mol/L Ca²⁺ inhibits its activity. The hydrolysis of tetrathionate (TT) by TTH_Mc results in the production of thiosulfate, pentathionate, and hexathionate. This study represents the first description of TTH in the genus Metallosphaera, providing new theoretical insights into the study of sulfur-oxidizing proteins in acidothermophilic archaea.

Tetrathionate hydrolase (TTH) is a key enzyme for oxidation of reduced inorganic sulfur compounds (RISCs) with S4I pathway, which is distributed in autotrophic or facultative auto-trophic sulfur-oxidizing bacteria and archaea. In this study, the enzyme TTHMc from the aci-dothermophilic archaeon Metallosphaera cuprina Ar-4T, encoded by mcup_1281 and belonging to the pyrroloquinoline quinone (PQQ) family, has been shown to possess tetrathionate hydrolysis ac-tivity. The molecular mass of the single subunit of TTHMc was determined to be 57 kDa. TTHMc is proved to locate in the cytoplasm, periplasmic space, and membrane, the activity of them ac-counted for 72.3%, 24.0%, and 3.7% of the total activity. Optimal activity was observed at tem-peratures above 95 °C and pH 6.0, the kinetic constants Km and Vmax were 0.35 mmol/L and 8.63 μmol/L, respectively. The presence of 0.01 mol/L Mg2+ enhances the activity of TTHMc, while 0.01 mol/L Ca2+ inhibits its activity. The hydrolysis of tetrathionate (TT) by TTHMc results in the pro-duction of thiosulfate, pentathionate, and hexathionate. This study represents the first description of TTH in the genus Metallosphaera, providing new theoretical insights into the study of sul-fur-oxidizing proteins in acidothermophilic archaea.