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 the year 2000.
- Acidithiobacillus ferrooxidans (syn. Thiobacillus ferrooxidans) lives in pyrite deposits, metabolizing iron and sulfur and producing sulfuric acid.
- Acidithiobacillus thiooxidans (syn. Thiobacillus thiooxidans, Thiobacillus concretivorus) consumes sulfur and produces sulfuric acid. Though first isolated from the soil it has also been observed causing biogenic sulfide corrosion of concrete sewer pipes by altering hydrogen sulfide sewage gas into sulfuric acid.
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. It is also used in the biomining process.
Genus Thiobacillus 
Thiobacillus 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.
Among the group of Thiobacilli, Thiobacillus ferrooxidans has emerged as an economically significant bacterium in the field of leaching of sulfide ores since its discovery in 1950 by Colmer et al. The discovery of T. 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- etc. (Torma, 1980). Acidithiobacillus 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.
Acidithioacillus ferrooxidans is an autotrophic, acidophilic, mesophile occurring in single or occasionally in pairs or chains, depending on growth conditions. Highly motile strains have been described as well as non-motile ones. Recent evidence indicate a high degree of genetic heterogeneity within the Acidithiobacillus ferrooxidans isolates, which are still probably misleadingly classified as a single species. Motile strains have a single flagellum & pili. The bacterium is non sporing and has a genome of about 2.8 × 106 base pairs and 55-65% of G-C content. Acidthiobacillus 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.
This genus and possibly the other genus in the order Acidithiobacillales (i.e. Thermithiobacillus) were formerly members of the Gammaproteobacteria but have now been reclassified into the Acidithiobacillia.
See also 
- Kelly, D.P., and Wood, A.P. (2000). "Reclassification of some species of Thiobacillus to the newly designated genera Acidithiobacillus gen. nov., Halothiobacillus gen. nov. and Thermithiobacillus gen. nov.". Int. J. Syst. Evol. Microbiol. 50 (2): 511–6.
- Selman A. Waksman and J.S. Joffe (1922). "Microorganisms Concerned in the Oxidation of Sulfur in the Soil II. Thiobacillus Thiooxidans, a New Sulfur-oxidizing Organism Isolated from the Soil". J Bacteriol 7 (2): 239–256. PMC 378965. PMID 16558952. 
- Sand, W. & Bock, E. (1987). "Biotest System For Rapid Evaluation Of Concrete Resistance To Sulfur-Oxidizing Bacteria". Materials Performance 26 (3): 14–17. 
- Acidithiobacillales entry in LPSN [Euzéby, J.P. (1997). "List of Bacterial Names with Standing in Nomenclature: a folder available on the Internet". Int J Syst Bacteriol 47 (2): 590–2. doi:10.1099/00207713-47-2-590. ISSN 0020-7713. PMID 9103655.]
- Williams, K. P.; Kelly, D. P. (2013). "Proposal for a new Class within the Proteobacteria, the Acidithiobacillia, with the Acidithiobacillales as the type Order". International Journal of Systematic and Evolutionary Microbiology. doi:10.1099/ijs.0.049270-0. PMID 23334881.