Key Laboratory of Water and Sediment Sciences, Ministry of Education, Department of Environmental Engineering, Peking University, Beijing, China.
Department of Geoscience, University of Calgary, Calgary, AB, Canada.
Environ Microbiol Rep. 2022 Oct;14(5):812-821. doi: 10.1111/1758-2229.13101. Epub 2022 Jun 12.
Microbial nitrate reduction can be driven by organic carbon oxidation, as well as by inorganic electron donors, such as reduced forms of sulfur and iron. An apparent inverse oxygen isotope fractionation effect was observed during nitrate reduction in sediment incubations from five sampling sites of a freshwater lake, Hongze Lake, China. Incubations with organic and inorganic electron donor additions were performed. Especially, the inverse oxygen isotope effect was intensified after glucose addition, whereas the incubations with sulfide and Fe showed normal fractionation factors. Nitrate reductase encoding genes, napA and narG, were analysed with metagenomics. Higher napA/narG ratios were associated with higher oxygen fractionation factors. The most abundant clade (59%) of NapA in the incubation with glucose was affiliated with Rhodocyclales. In contrast, it only accounted for 8%-9% of NapA in the incubations with sulfide and Fe . Differences in nitrate reductases might explain different oxygen isotope effects. Our findings also suggested that large variance of O-nitrate isotope fractionations might have to be considered in the interpretation of natural isotope records.
微生物的硝酸盐还原可以由有机碳氧化以及无机电子供体（如硫和铁的还原形式）驱动。在中国洪泽湖五个采样点的沉积物培养中，观察到硝酸盐还原过程中存在明显的氧同位素分馏效应。进行了有机和无机电子供体添加的培养。特别是，葡萄糖添加后，逆氧同位素效应加剧，而硫化物和 Fe 的培养则表现出正常的分馏因子。用宏基因组学分析了硝酸盐还原酶编码基因 napA 和 narG。较高的 napA/narG 比值与较高的氧分馏因子相关。在葡萄糖培养中最丰富的 NapA 分支（59%）与 Rhodocyclales 有关。相比之下，它在硫化物和 Fe 的培养中仅占 NapA 的 8%-9%。硝酸盐还原酶的差异可能解释了不同的氧同位素效应。我们的研究结果还表明，在解释自然同位素记录时，必须考虑 O-硝酸盐同位素分馏的大方差。
