Acidithiobacillus thiooxidans
Taxonomy and Phylogeny
Acidithiobacillus thiooxidans is a Gram-negative, rod-shaped bacterium belonging to the Proteobacteria phylum. It is classified under the Acidithiobacillus genus, which consists of acidophilic, obligately chemolithotrophic bacteria that derive energy from the oxidation of reduced inorganic sulfur compounds (RISCs). This genus was previously part of the Thiobacillus genus before being reclassified based on 16S rRNA gene sequence analysis.
Morphology and Physiology
Acidithiobacillus thiooxidans cells are rod-shaped and measure approximately 0.5-1.0 μm in diameter and 1.0-1.5 μm in length. They are motile via a single polar flagellum. The bacterium is an obligate aerobe, meaning it requires oxygen to survive. It is also an acidophile, thriving in extremely acidic environments with a pH range of 1.0-5.0, with an optimum pH of 2.0.
Metabolism
Acidithiobacillus thiooxidans is a chemolithoautotroph, obtaining energy from the oxidation of inorganic sulfur compounds such as elemental sulfur, thiosulfate, and tetrathionate. The energy derived from these reactions is used to fix carbon dioxide into organic compounds via the Calvin-Benson-Bassham cycle, a process known as autotrophic carbon fixation.
Ecological Significance
Acidithiobacillus thiooxidans plays a crucial role in the sulfur cycle, one of the biogeochemical cycles that are essential for life on Earth. It contributes to the formation of acid mine drainage (AMD), a major environmental problem associated with mining activities. Despite its destructive potential, A. thiooxidans is also used in bioleaching, a process that uses bacteria to extract metals from ores.
Industrial Applications
Acidithiobacillus thiooxidans is used in the mining industry for the bioleaching of sulfide ores. This process is environmentally friendly compared to traditional smelting methods, as it reduces the emission of sulfur dioxide, a potent greenhouse gas. The bacterium is also used in the treatment of sewage and industrial waste containing sulfur compounds.
Genomics
The genome of Acidithiobacillus thiooxidans has been sequenced, providing insights into its metabolic capabilities and its adaptation to extreme environments. The bacterium has a single circular chromosome of approximately 3.9 Mb, with a GC content of around 53%.