Catalyzes the oxidation of 2 molecules of thiosulfate to tetrathionate, using TsdB as an electron acceptor. 2 Fe(III)-[cytochrome c] + 2 thiosulfate = 2 Fe(II)-[cytochrome c] + 2 H(+) + tetrathionate Monomer. Binds 2 heme c groups covalently per subunit.