Dualism of denitrification and dissimilatory nitrate reduction to ammonium in sediment of nitrate-polluted aquatic ecosystems

沉积物细菌的异化硝酸盐还原作用是促进水体富营养化的最重要的硝酸盐库。令人费解的是，在大多数情况下，只有将硝酸盐转化为氮气的反硝化（DEN）才是研究的主题。然而，在这项研究中，异化硝酸盐还原为铵（DNRA），这可能是在许多水生生态系统的定量重要，将进行调查。DNRA对富营养化无效，因为产生的铵被保存在生态系统中。本研究的中心目标是对DNRA和DEN进行比较和公平的调查，以便更好地了解控制非生物因素（例如，硝酸盐、硫化物、有机碳、铁）。在一种新的方法中，DNRA和DEN在沉积物中的垂直分布将用微传感器，凝胶探针和质谱分析。利用分子生物学技术，从功能基因（亚硝酸盐还原酶）水平研究硝酸盐还原菌群的组成和活性。将在相关实地验证利用底栖梯度室、自然沉积物和细菌分离物进行的实验室实验所获得的结果。

Dissimilatory nitrate reduction by sediment bacteria is the quantitatively most important sink for nitrate that promotes the eutrophication of aquatic ecosystems. Incomprehensibly, in most cases only denitrification (DEN) that converts nitrate into nitrogen gas has been subject of research. In this study, however, the dissimilatory nitrate reduction to ammonium (DNRA), which maybe is quantitatively important in many aquatic ecosystems, will be investigated. DNRA is not effective against eutrophication because the ammonium produced is preserved in the ecosystem. The central goal of this study is the comparative and equitable investigation of DNRA and DEN in order to better understand the controlling abiotic factors (e.g., nitrate, sulfide, organic carbon, iron). In a novel approach, the vertical distribution of both DNRA and DEN in the sediment will be analysed with microsensors, gel probes, and mass spectrometry. Abundance and activity of the nitrate-reducing microbial community will be studied on the level of functional genes (here: nitrite reductases) with molecular techniques. Results obtained in laboratory experiments using benthic gradient chambers, natural sediments, and bacterial isolates will be validated at relevant field sites.