The Acidithiobacillales are an order within the Class Acidithiobacillia and comprises the genera Acidithiobacillus and Thermithiobacillus. Originally both were included in the genus Thiobacillus, but they are not related to the type species, which belongs to the beta proteobacteria.
^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. PMID23334881.edit
^Kelly (D.P.) and Wood (A.P.): Reclassification of some species of Thiobacillus to the newly designated genera Acidithiobacillus gen. nov., Halothiobacillus gen. nov. and Thermithiobacillus gen. nov. In: International Journal of Systematic and Evolutionary Microbiology, 2000, 50, 511-516.