Evidence and quantification of thiosulfate reducers unable to reduce sulfate in ricefield soils

We provide the first evidence that thiosulfate reduction can be performed in soil under anaerobic conditions by nonsulfate- reducing bacteria. Culturable thiosulfate-reducing bacteria were enumerated in live ricefield soils by MPN counts, using peptides and H, as energy sources, and thiosulfate as the electron acceptor. Such conditions favoured the growth of (i) thiosulfatereducing bacteria unable to use sulfate as electron acceptor and (ii) sulfate-reducing bacteria that did not use lactate as an energy source. Thiosulfate-reducing bacteria ranged from 40 to 4. IO4 cells& dry soil and their abundance was of the same order of magnitude as that of sulfate reducers using lactate. Most probably, thiosulfate-reducing bacteria unable to use sulfate are as important as sulfate reducers for sulfur cycling in some wetland soils