Antimony Isotope Fractionation During Kinetic Sb(III) Oxidation by Antimony-Oxidizing Bacteria Pseudomonas Sp. J1.

Antimony (Sb) isotopic fractionation is frequently used as a proxy for biogeochemical processes in nature. However, to date, little is known about Sb isotope fractionation in biologically driven reactions. In this study, Pseudomonas sp. J1 was selected for Sb isotope fractionation experiments with varying initial Sb concentration gradients (50-200 mu M) at pH 7.2 and 30 degrees C. Compared to the initial Sb(III) reservoir (delta Sb-123 = 0.03 +/- 0.01 similar to 0.06 +/- 0.01 parts per thousand), lighter isotopes were preferentially oxidized to Sb(V). Relatively constant isotope enrichment factors (epsilon) of -0.62 +/- 0.06 and -0.58 +/- 0.02 parts per thousand were observed for the initial Sb concentrations ranging between 50 and 200 mu M during the first 22 days. Therefore, the Sb concentration has a limited influence on Sb isotope fractionation during Sb(III) oxidation that can be described by a kinetically dominated Rayleigh fractionation model. Due to the decrease in the Sb-oxidation rate by Pseudomonas sp. J1, observed for the initial Sb concentration of 200 mu M, Sb isotope fractionation shifted toward isotopic equilibrium after 22 days, with slightly heavy Sb(V) after 68 days. These findings provide the prospect of using Sb isotopes as an environmental tracer in the Sb biogeochemical cycle.