Dissimilatory nitrate reduction to ammonia (DNRA) process, competing with denitrification and anaerobic ammonia oxidation (anammox) for nitrate, is an important nitrogen retention pathway in the environment. Previous studies on DNRA bacterial diversity and composition focused on the surface sediments in estuaries, but studies on the deep sediments are limited, and the linkage between DNRA community structure and complex estuarine environment remains unclear. In this study, through high-throughput sequencing of nrfA gene followed by high-resolution sample inference, we examined spatially and temporally the composition and diversity of DNRA bacteria along a salinity gradient in five sediment cores of the Pearl River Estuary (PRE). We found a higher diversity and richness of DNRA bacteria in sediments with lower organic carbon, where sea water intersects fresh water. Moreover, the DNRA bacterial communities had the specific spatially distribution coupling with their metabolic difference along the salinity gradient of the Pearl River Estuary, but no obvious difference along the sediment depth. The distribution of DNRA bacteria in the PRE was largely driven by various environmental factors, including salinity, Oxidation-Reduction Potential (ORP), ammonium, nitrate and C_org/NO₃⁻. Furthermore, dominant DNRA bacteria were found to be the key populations of DNRA communities in the PRE sediments by network analysis. Collectively, our results showed that niche difference of DNRA bacteria indeed occurs in the Pearl River Estuary.

硝酸盐异化还原成氨 (DNRA) 过程与反硝化和厌氧氨氧化 (anammox) 竞争硝酸盐，是环境中重要的氮保留途径。以往对DNRA细菌多样性和组成的研究主要集中在河口表层沉积物，但对深层沉积物的研究有限，DNRA群落结构与复杂河口环境之间的联系尚不清楚。本研究通过高通量测序nrfA基因，然后进行高分辨率样本推断，我们在空间和时间上检查了珠江口 (PRE) 五个沉积物核心中 DNRA 细菌沿盐度梯度的组成和多样性。我们发现，在海水与淡水相交的有机碳含量较低的沉积物中，DNRA 细菌的多样性和丰富度更高。此外，DNRA细菌群落沿珠江口盐度梯度具有特定的空间分布与其代谢差异耦合，但沿沉积物深度无明显差异。DNRA 细菌在 PRE 中的分布主要受各种环境因素驱动，包括盐度、氧化还原电位 (ORP)、铵、硝酸盐和 C _org /NO ₃ ^-. 此外，通过网络分析发现优势 DNRA 细菌是 PRE 沉积物中 DNRA 群落的关键种群。总的来说，我们的结果表明，珠江口确实存在DNRA细菌的生态位差异。