[Fractionation of stable isotopes of sulfur during its oxidation by Thiobacillus ferrooxidans]

The fractionation of sulfur isotopes was studied in the process of sulfur oxidation by Thiobacillus ferrooxidans. The isotope effect was observed at all stages of the bacterial growth during sulfur oxidation; as a result, residual sulfur became heavier whereas the fraction of colloidal sulfur and the fraction of sulfates became lighter. The isotope differences between the residual sulfur and the sulfates were greatest at the end of the lag phase (delta 34S = 0.38%) and the beginning of the stationary phase of the cultural growth (delta 34S = 0.34%). As was shown in model experiments, the phospholipids lecithin and cephalin can dissolve sulfur and form products enriched in 32S(delta 34S = -0.51 -1.60%). The mechanism of oxidation of elementary sulfur by Thiobacillus ferrooxidans is discussed.