Abstract：
The mechanism governing sulfur cycling in nitrate reduction within sulfate-rich reservoirs during seasonal hypoxic conditions remains poorly understood. This study employs nitrogen and oxygen isotope fractionation in nitrate, along with metagenomic sequencing to elucidate the intricacies of the coupled sulfur oxidation and nitrate reduction process in the water column. In the Aha reservoir, a typical seasonally stratified water body, we observed the coexistence of denitrification, bacterial sulfide oxidation, and bacterial sulfate reduction in hypoxic conditions. This is substantiated by the presence of abundant N/S-related genes (nosZ and aprAB/dsrAB) and fluctuations in N/S species. The lower 15εNO3/18εNO3 ratio (0.60) observed in this study, compared to heterotrophic denitrification, strongly supports the occurrence of sulfur-driven denitrification. Furthermore, we found a robust positive correlation between the metabolic potential of bacterial sulfide oxidation and denitrification (p < 0.05), emphasizing the role of sulfide produced via sulfate reduction in enhancing denitrification. Sulfide-driven denitrification relied on ∑S2- as the primary electron donor preferentially oxidized by denitrification. The pivotal genus, Sulfuritalea, emerged as a central player in both denitrification and sulfide oxidation processes in hypoxic water bodies. Our study provides compelling evidence that sulfides assume a critical role in regulating denitrification in hypoxic water within an ecosystem where their contribution to the overall nitrogen cycle was previously underestimated.
摘要：
在季节性低氧条件下，控制富含硫酸盐的水库中硝酸盐还原中硫循环的机制尚不清楚。这项研究采用硝酸盐中的氮和氧同位素分馏，以及宏基因组测序，以阐明水柱中硫氧化和硝酸盐还原过程的复杂性。在阿哈水库，典型的季节性分层水体，我们观察到反硝化共存，细菌硫化物氧化，在低氧条件下减少细菌硫酸盐。丰富的N/S相关基因（nosZ和aprAB/dsrAB）的存在以及N/S物种的波动证实了这一点。在这项研究中观察到较低的15εNO3/18εNO3比率(0.60)，与异养反硝化相比，有力地支持了硫驱动反硝化的发生。此外，我们发现细菌硫化物氧化和反硝化的代谢潜力之间存在强正相关（p<0.05），强调通过硫酸盐还原产生的硫化物在增强反硝化中的作用。硫化物驱动的反硝化依赖于∑S2-作为优先被反硝化氧化的主要电子供体。关键属，硫磺,在低氧水体中的反硝化和硫化物氧化过程中都是中心角色。我们的研究提供了令人信服的证据，表明硫化物在调节生态系统中低氧水中的反硝化中起着至关重要的作用，而以前它们对整个氮循环的贡献被低估了。
