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要旨

The isotopic fractionation during bacterial sulfate reduction was determined in batch culture experiments with new strains of sulfate-reducing bacteria that grow at temperatures between -1.8 and 20 degrees C. The observed isotopic fractionations for the two isolates are significantly smaller than commonly measured isotopic differences between sulfate and sulfide in temperate and cold marine sediments. For all cultures, sulfate reduction rates decrease with decreasing temperature. However, in one strain the isotopic fractionation was independent of the sulfate reduction rates and the temperature at which the bacteria were grown whereas another culture showed an increasing isotopic fractionation with decreasing temperature. Phylogenetic differences between the strains, differences in the cellular electron transport pathways during substrate oxidation, and the formation of sulfur intermediates at very low rates of sulfate reduction are inferred to be the dominating factors controlling the observed isotopic fractionations.