Summary auto-generated
This paper presents a taxonomic reclassification of eight Thiobacillus species into three newly designated genera based on 16S rRNA gene sequencing and physiological analysis. The original Thiobacillus genus was highly heterogeneous, with species distributed across multiple proteobacterial subclasses (α, β, and γ). The type species, Thiobacillus thioparus, remains in the β-subclass, while eight γ-subclass species are reassigned. Four acidophilic species form the new genus Acidithiobacillus, which includes T. thiooxidans, T. ferrooxidans, T. caldus, and T. albertensis; these bacteria oxidize reduced sulfur compounds and some also oxidize iron. Three halotolerant or halophilic species constitute the new genus Halothiobacillus (T. neapolitanus, T. halophilus, and T. hydrothermalis), which tolerate high salt concentrations. A single moderately thermophilic species forms Thermithiobacillus tepidarius. All reclassified species are obligately chemolithoautotrophic, gram-negative rods that obtain energy from inorganic sulfur oxidation. This reclassification addresses longstanding taxonomic confusion by reflecting genetic and physiological diversity that had previously been masked under a single genus name.
Key findings
- Eight Thiobacillus species are reclassified into three new genera (Acidithiobacillus, Halothiobacillus, and Thermithiobacillus) based on 16S rRNA sequences and physiology
- Acidithiobacillus comprises four acidophilic species; some oxidize ferrous iron or metal sulfides in addition to reduced sulfur compounds
- Halothiobacillus contains three halotolerant to halophilic species tolerating high salt concentrations
- The original Thiobacillus type species (T. thioparus) remains in the β-subclass, while reclassified species belong to the γ-subclass of Proteobacteria
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Abstract
The species of the genus 'Thiobacillus' fall into the alpha-, beta- and gamma-subclasses of the Proteobacteria, the type species Thiobacillus thioparus being located in the beta-subclass. 'Thiobacillus' species exhibit almost as much diversity in DNA composition and physiology as is found collectively in all other proteobacterial groups. On the basis of physiological characters and 16S rRNA gene sequence comparisons, eight of the existing Thiobacillus species are proposed for reassignment to three newly designated genera within the gamma-subclass of the Proteobacteria, namely Acidithiobacillus, Halothiobacillus and Thermithiobacillus.