NOVEL PROCESSES FOR ANAEROBIC SULFATE PRODUCTION FROM ELEMENTAL SULFUR BY SULFATE-REDUCING BACTERIA

Sulfate reducers and related organisms which had previously been found to reduce Fe(III) with H-2 or organic electron donors oxidized S-0 to sulfate when Mn(IV) was provided as an electron acceptor. Organisms c atalyzing this reaction in washed cell suspensions included Desulfovib rio desulfuricans, Desulfomicrobium baculatum, Desulfobacterium autotr ophicum, Desulfuromonas acetoxidans, and Geobacter metallireducens. Th ese organisms produced little or no sulfate from S-0 with Fe(III) as a potential electron acceptor or in the absence of an electron acceptor . In detailed studies with Desulfovibrio desulfuricans, the stoichiome try of sulfate and Mn(II) production was consistent with the reaction S-0 + 3 MnO2 + 4H(+)-->SO42- + 3Mn(II) + 2H(2)O. None of the organisms evaluated could be grown with S-0 as the sole electron donor and Mn(I V) as the electron acceptor. In contrast to the other sulfate reducers evaluated, Desulfobulbus propionicus produced sulfate from S-0 in the absence of an electron acceptor and Fe(III) oxide stimulated sulfate production. Sulfide also accumulated in the absence of Mn(IV) or Fe(II I). The stoichiometry of sulfate and sulfide production indicated that Desulfobulbus propionicus disproportionates S-0 as follows: 4S(0) + 4 H(2)O-->SO42 + 3HS(-) + 5 H+. Growth of Desulfobulbus propionicus with SO as the electron donor and Fe(III) as a sulfide sink and/or electro n acceptor was very slow. The S-0 oxidation coupled to Mn(IV) reductio n described here provides a potential explanation for the Mn(TV)-depen dent sulfate production that previous studies have observed in anoxic marine sediments. Desulfobulbus propionicus is the first example of a pure culture known to disproportionate S-0.