Abstract：
Anaerobic ammonium oxidation (anammox) has been widely used for the sustainable removal of nitrogen from wastewater. Extracellular DNA (exDNA), as one of the main components of biofilms, not only determines the initial formation process, but also allows the three-dimensional structure to be maintained. Since the effects of exDNA on anammox biofilm formation are still poorly understood, this study elucidated the effects of exDNA on different stages of anammox biofilm establishment and maintenance under static conditions and its mechanism. The results revealed that exDNA mainly affected the maintenance stage of anammox biofilm formation. Compared with the absence of exDNA, nitrogen removal efficiency in the presence of exDNA was 6.17 % higher; the number of bacteria cells attached to the carrier was 2.23 times that in the absence of exDNA. The spatiotemporal distribution of bacteria was revealed by fluorescence in situ hybridization. After 30 days, the relative abundances of anammox in biofilms were 6.19 % and 0.4 % in the presence and absence of exDNA, respectively, indicating its positive role in anammox bacteria (AnAOB) adhesion and biofilm formation. The presence of exDNA in extracellular polymeric substances (EPS) promotes the synthesis of proteins and soluble microbial products. According to the extended Derjaguin-Landau-Verwey-Overbeek (X - DLVO) theory, the presence of exDNA also reduced the Lewis acid-base interaction energy and created favorable thermodynamic conditions for AnAOB adhesion. These findings advance our understanding of the role of exDNA in anammox-mediated biofilm formation and offer insights into the mechanism of exDNA in the establishment and maintenance stages.
摘要：
厌氧氨氧化（anammox）已广泛用于废水中氮的可持续去除。细胞外DNA(exDNA),作为生物膜的主要成分之一，不仅决定了最初的形成过程，而且还可以保持三维结构。由于exDNA对anammox生物膜形成的影响仍然知之甚少，本研究阐明了在静态条件下，exDNA对厌氧氨氧化生物膜建立和维持不同阶段的影响及其机制。结果表明，exDNA主要影响厌氧氨氧化生物膜形成的维持阶段。与缺乏exDNA相比，在存在exDNA的情况下，脱氮效率提高了6.17％；附着在载体上的细菌细胞数量是没有exDNA的情况下的2.23倍。通过荧光原位杂交揭示了细菌的时空分布。30天后,在存在和不存在exDNA的情况下，生物膜中厌氧氨氧化的相对丰度分别为6.19%和0.4%，分别,表明其在厌氧氨氧化细菌（AnAOB）粘附和生物膜形成中的积极作用。胞外聚合物（EPS）中exDNA的存在促进了蛋白质和可溶性微生物产物的合成。根据扩展的Derjaguin-Landau-Verwey-Overbeek(X-DLVO)理论，exDNA的存在也降低了Lewis酸碱相互作用能并为AnAOB粘附创造了有利的热力学条件。这些发现促进了我们对exDNA在anammox介导的生物膜形成中的作用的理解，并提供了对exDNA在建立和维持阶段的机制的见解。
