Thiobacillus

Thiobacillus is a genus of Gram-negative Betaproteobacteria. Thiobacillus thioparus is the type species of the genus, and the type strain thereof is the Starkey^T strain, isolated by Robert Starkey in the 1930s from a field at Rutgers University in the United States of America. While over 30 "species" have been named in this genus since it was defined by Martinus Beijerinck in 1904,^[1][2] (the first strain was observed by the biological oceanographer Alexander Nathansohn in 1902 - likely what we would now call Halothiobacillus neapolitanus^[3]), most names were never validly or effectively published. The remainder were either reclassified into Paracoccus, Starkeya (both in the Alphaproteobacteria); Sulfuriferula, Annwoodia, Thiomonas (in the Betaproteobacteria); Halothiobacillus, Guyparkeria (in the Gammaproteobacteria), or Thermithiobacillus or Acidithiobacillus (in the Acidithiobacillia). The very loosely defined "species" Thiobacillus trautweinii was where sulfur oxidising heterotrophs and chemolithoheterotrophs were assigned in the 1910-1960s era, most of which were probably Pseudomonas species.^[4] Many species named in this genus were never deposited in service collections and have been lost.^[4][3]

All species are obligate autotrophs^[1][2][3] (using the transaldolase form of the Calvin-Benson-Bassham cycle^[4]) using elementary sulfur, thiosulfate, or polythionates as energy sources - the former Thiobacillus aquaesulis can grow weakly on complex media as a heterotroph, but has been reclassified to Annwoodia aquaesulis. Some strains (E6 and Tk-m) of the type species Thiobacillus thioparus can use the sulfur from dimethylsulfide, dimethyldisulfide, or carbon disulfide to support autotrophic growth - they oxidise the carbon from these species into carbon dioxide and assimilate it. Sulfur oxidation is achieved via the Kelly-Trudinger pathway.