Accumulation of sulfite by a sulfate-using revertant of Salmonella pullorum

Sulfate-utilizing revertants of a cysteine auxotroph of Salmonella pullorum have been found that cause an accumulation in growth medium of a sulfur compound more oxidized than sulfide. The sulfur compound was presumptively identified as sulfite by the formation of a colored complex in the presence of basic fuchsin and formaldehyde, oxidation to sulfate by peroxide, and acid-volatility. The acid-volatile material was identified as sulfite by formation of an S-sulfonyl derivative of 5,5'-dithio-bis(2-nitrobenzoic acid) which was chromatographically and electrophoretically identical to an authentic S-sulfonyl derivative. The presence of sulfate in minimal medium is required for sulfite accumulation, and both cysteine and selenate inhibit the accumulation. No evidence was obtained to indicate that a reduced sulfur compound was the precursor of the accumulated sulfite.