Effect of NO2− on Stable Isotope Fractionation during Bacterial Sulfate Reduction

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• 作者：Florian Einsiedl
• 刊名：Environmental Science & Technology
• 出版年：2009
• 出版时间：January 1, 2009
• 年：2009
• 卷：43
• 期：1
• 页码：82-87
• 全文大小：198K
• 年卷期：v.43,no.1(January 1, 2009)
• ISSN：1520-5851

文摘

The effects of low NO₂⁻ concentrations on stable isotope fractionation during dissimilatory sulfate reduction by strain Desulfovibrio desulfuricans were investigated. Nitrite, formed as an intermediate during nitrification and denitrification processes in marine and freshwater habitats, inhibits the reduction of the sulfuroxy intermediate SO₃²⁻ to H₂S even at low concentrations. To gain an understanding of the inhibition effect of the reduction of the sulfuroxy intermediate on stable isotope fractionation in sulfur and oxygen during bacterial sulfate reduction, nitrite was added in the form of short pulses. In the batch experiments that contained 0.02, 0.05, and 0.1 mM nitrite, sulfur enrichment factors ε of −12 ± 1.6, −15 ± 1.1, and −26 ± 1.3‰, respectively were observed. In the control experiment (no addition of nitrite) a sulfur enrichment factor ε of around −11‰ was calculated. In the experiments that contained no ¹⁸O enriched water (δ¹⁸O: −10‰) and nitrite concentrations of 0.02, 0.05, and 0.1 mM, δ¹⁸O values in the remaining sulfate were fairly constant during the experiments (δ¹⁸O sulfate: ≈10‰) and were similar to those obtained from the control experiment (no nitrite and no enriched water). However, in the batch experiments that contained ¹⁸O enriched water (+700‰) and nitrite concentrations of 0.05 and 0.1 mM increasing δ¹⁸O values in the remaining sulfate from around 15‰ to approximately 65 and 85‰, respectively, were found. Our experiments that contained isotopic enriched water and nitrite show clear evidence that the ratio of forward and backward fluxes regulated by adenosine-5′-phosphosulfate reductase (APSR) controls the extent of sulfur isotope fractionation during bacterial sulfate reduction in strain Desulfovibrio desulfuricans. Since the metabolic sulfuroxy intermediate SO₃²⁻ exchanges with water, evidence of ¹⁸O enriched water in the remaining sulfate in the experiments that contained nitrite also demonstrates that SO₃²⁻ recycling to sulfate affects sulfur and oxygen isotope fractionation during bacterial sulfate reduction to some extent. Even though reduction of adenosine-5′-phosphosulfate (APS) to sulfite of −25‰ was not fully expressed, SO₃²⁻ was recycled to SO₄²⁻. On the basis of the results of this study a sulfur isotope fractionation for APSR of up to approximately −30‰ can be assumed. However, reported NO₂⁻ concentrations of up to 20 μM in freshwater and marine habitats may not significantly impact the ability to use stable isotope analysis in assessing bacterial sulfate reduction.