Summary In this work we identified the gene for the tetrathionate‐forming thiosulfate dehydrogenase (TsdA) from the purple sulfur bacterium Allochromatium vinosum by sequence analysis and reverse genetics. The recombinant protein produced in Escherichia coli is a periplasmic, monomeric 25.8 kDa dihaem cytochrome c with an enzyme activity optimum at pH 4. UV‐visible and electron paramagnetic resonance spectroscopy indicate meth...