Acidithiobacillus sibiricus sp. nov., a novel extremely acidophilic sulfur-oxidizing bacterium isolated from a magmatic sulfide-rich ore deposit

Abstract

A new motile, extremely acidophilic, halotolerant, facultatively neutrophilic, mesophilic, thermotolerant bacterial strain A1 was isolated from a polymetallic sulfidic ore. Its exceptional S⁰-oxidizing capacity supported growth between 20 and 43 °C (optimum, 30–35 °C) and across a broad pH range (0.4 to 6.5), with an optimum at pH 2.5–2.6. A notable feature of strain A1 was the formation of large cell conglomerates (0.1–0.2 mm) on sulfur particles. Electron microscopy revealed a single polar flagellum, carboxysomes, and storage granules. Strain A1 also grew on thiosulfate and tetrathionate but showed no growth with ferrous iron or under obligately heterotrophic conditions. Phylogenetically, strain A1 clustered with Acidithiobacillus acidisediminis, forming a distinct lineage within the genus Acidithiobacillus. Chemotaxonomic analysis identified C_16:0, C_18:0, and C_18:1ω9c fatty acids, ubiquinone-8 as the major respiratory quinone, and characteristic polar lipids. Complete genome analysis revealed sulfur oxidation pathways and carboxysome-related genes, along with a conjugative plasmid encoding a type IV secretion system and genes potentially involved in biofilm formation and metal/redox response. The chromosome carried systems for metal(loid) resistance and a complete glutathione redox cycle, indicating strong adaptation to oxidative and metal stress in acidic environments. Based on these characteristics, Acidithiobacillus sibiricus sp. nov. is proposed, with strain A1 as the type strain (=KCTC 8561ᵀ = CGMCC 1.62200ᵀ). Sequence-based analyses indicate that At. sibiricus is abundant in the original sulfidic ore community and occurs across multiple environments and geographic regions.