Purpose

Dissimilatory nitrate (NO₃⁻) reduction to ammonium (DNRA) is a significant nitrogen (N) transformation process in estuarine ecosystem. The objectives of this study were to clarify the key biotic and abiotic factors influencing DNRA potential rates in Xiamen Bay.

Methods

We characterized DNRA, anammox, and denitrification rates through ¹⁵ N isotope tracer experiments. Then quantitative real-time PCR and high-throughput sequencing analysis were conducted to analyze the abundance and community of DNRA bacteria. Spearman correlation analysis was used to understand the relationships of DNRA rate, nrfA abundance, and community with environmental characteristics.

Results

Denitrification was dominated in dissimilatory NO₃⁻ reduction processes in sediments of Xiamen Bay. Bacteroidetes and Proteobacteria were the main phyla of DNRA bacteria and Pelobacter was the dominant genus. Spearman correlation analysis showed that DNRA rate was significantly positively correlated with nitrite (NO₂⁻) and NO₃⁻ in interstitial water, total organic carbon (TOC), acid volatile sulfide (AVS), and total nitrogen (TN) in sediment. Besides, nrfA abundance showed positive correlations with DNRA rate, NO₂⁻, TOC, AVS, and TN. Furthermore, AVS and nrfA abundance were positively correlated with Pelobacter.

Conclusion

DNRA rates were limited by sulfide, organic carbon, abundances of nrfA gene, and DNRA bacteria. Sulfide and organic carbon shaped DNRA bacterial community thereby controlled DNRA rate. Heterotrophic sulfide-producing genus (Pelobacter) prevailed among DNRA bacteria, which might support autotrophic DNRA bacteria. In this way, heterotrophic and autotrophic DNRA bacteria were connected through sulfide-producing genus and acted as a whole functional community.

中文翻译：

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DNRA 受到厦门湾沉积物中硫化物和 nrfA 丰度的限制，其中 DNRA 细菌中存在异养硫化物产生属（Pelobacter）

目的

异化硝酸盐（NO ₃ ^-）还原为铵（DNRA）是河口生态系统中重要的氮（N）转化过程。本研究的目的是阐明影响厦门湾 DNRA 潜在率的关键生物和非生物因素。

方法

我们通过¹⁵  N 同位素示踪剂实验表征了 DNRA、厌氧氨氧化和反硝化率。然后进行定量实时PCR和高通量测序分析，分析DNRA细菌的丰度和群落。通过Spearman相关分析了解DNRA率、nrf A丰度、群落与环境特征的关系。

结果

厦门湾沉积物中异化NO ₃ ^-还原过程以反硝化作用为主。拟杆菌门和变形菌门是 DNRA 细菌的主要门类，而Pelobacter是优势属。Spearman相关分析表明，DNRA率与间隙水中的亚硝酸盐（NO ₂ ^-）和NO ₃ ^-、总有机碳（TOC）、酸性挥发性硫化物（AVS）和沉积物中的总氮（TN）呈显着正相关。此外，nrf A丰度与DNRA率、NO ₂ ^-、TOC、AVS和TN呈正相关。此外，AVS 和nrf丰度与Pelobacter呈正相关。

结论

DNRA 率受到硫化物、有机碳、nrf A 基因丰度和 DNRA 细菌的限制。硫化物和有机碳塑造了 DNRA 细菌群落，从而控制了 DNRA 率。异养产硫化物属（Pelobacter）在DNRA细菌中占优势，这可能支持自养DNRA细菌。这样，异养和自养 DNRA 细菌通过产硫化物属连接起来，作为一个完整的功能群落。