Acidithiobacillus

Acidithiobacillus is a genus of Proteobacteria. Like all Proteobacteria, Acidithiobacillus is Gram-negative. The members of this genus used to belong to Thiobacillus, before they were reclassified in 2000.^[1]

• Acidithiobacillus ferrooxidans (syn. Thiobacillus ferrooxidans) lives in pyrite deposits, metabolizing iron and sulfur and producing sulfuric acid.
• Acidithiobacillus thiooxidans (syn. Thiobacillus thiooxidans, Thiobacillus concretivorus^[1]) consumes sulfur and produces sulfuric acid; first isolated from the soil,^[2] it has also been observed causing biogenic sulfide corrosion of concrete sewer pipes by altering hydrogen sulfide sewage gas into sulfuric acid.^[3]

Both of these bacteria are used in a mining technique called bioleaching whereby metals are extracted from their ores through oxidation. The bacteria are used as catalysts. They are also used in the biomining process.

Genus Acidithiobacillus

Acidithiobacillus is the most important genus of chemolithotrophs that metabolize sulfur. It includes motile, rod-shaped cells that can be isolated from rivers, canals, acidified sulfate soils, mine drainage effluents, and other mining areas. These thiobacilli are adapted to wide variations of temperature and pH and can be readily isolated and enriched.

Bioleaching

Among the group of acidithiobacilli, Acidithiobacillus ferrooxidans has emerged as an economically significant bacterium in the field of leaching of sulfide ores since its discovery in 1950 by Colmer, Temple and Hinkle. The discovery of A. ferrooxidans led to the development of a new branch of metallurgical sciences called “biohydrometallurgy”, which deals with all aspects of microbial mediated extraction of metals from minerals or solid wastes and acid mine drainage.^[4] A. ferrooxidans has been proven as a potent leaching organism, for dissolution of metals from low-grade sulfide ores. Recently, the attention has been focused upon the treatment of mineral concentrates, as well as complex sulfide ores using batch or continuous-flow reactors.

Morphology

A. ferrooxidans is an autotrophic, acidophilic, mesophile occurring in single cells or occasionally in pairs or chains, depending on growth conditions. Highly motile strains have been described, as well as nonmotile ones. Recent evidence indicates a high degree of genetic heterogeneity within the A. ferrooxidans isolates, which are still probably misleadingly classified as a single species. Motile strains have a single flagellum and pili. The bacterium is nonspore-forming and has a genome around 2.8 megabase pairs and 55-65% of G-C content. A. ferrooxidans grows at pH values of 4.5 to 1.3 in basal salt medium and derives its biosynthetic requirements by autotrophy using carbon from atmospheric carbon dioxide. Nitrogen fixation also is an important ecological function carried out by this bacterium in acidophilic habitats. Metabolic energy is derived aerobically by the oxidation of reduced inorganic sulfur compounds or ferrous ions. Anaerobic growth using elemental hydrogen or reduced inorganic sulfur compounds as electron donors and ferric ions as electron acceptors has also been discovered.

Phylogeny

This genus and possibly the other genus in the order Acidithiobacillales (i.e. Thermithiobacillus^[5]) were formerly members of the Gammaproteobacteria but have now been reclassified into the Acidithiobacillia.^[6]

See also

• Talvivaara mine

References

External links

• Acidithiobacillus ferrooxidans ATCC 23270 Genome Page
• Thiobacillus sp.