Nitrogen-cycling microorganisms play key roles at the intersection of microbiology and wastewater engineering. In addition to the well-studied ammonia oxidizing bacteria, nitrite oxidizing bacteria, heterotrophic denitrifiers, and anammox bacteria, there are some other N-cycling microorganisms that are less abundant but functionally important in wastewater nitrogen removal. These microbes include, but not limited to ammonia oxidizing archaea (AOA), complete ammonia oxidation (comammox) bacteria, dissimilatory nitrate reduction to ammonia (DNRA) bacteria, and nitrate/nitrite-dependent anaerobic methane oxidizing (NO_x-DAMO) microorganisms. In the past decade, the development of high-throughput molecular technologies has enabled the detection, quantification, and characterization of these minor populations. The aim of this review is therefore to synthesize the current knowledge on the distribution, ecological niche, and kinetic properties of these “overlooked” N-cycling microbes at wastewater treatment plants. Their potential applications in novel wastewater nitrogen removal processes are also discussed. A comprehensive understanding of these overlooked N-cycling microbes from microbiology, ecology, and engineering perspectives will facilitate the design and operation of more efficient and sustainable biological nitrogen removal processes.

氮循环微生物在微生物学和废水工程学的交集中起着关键作用。除了经过深入研究的氨氧化细菌，亚硝酸盐氧化细菌，异养反硝化剂和厌氧氨氧化细菌外，还有一些其他的N循环微生物，它们的含量较低，但在废水脱氮中具有重要的功能。这些微生物包括但不限于氨氧化古细菌（AOA），完全氨氧化（comammox）细菌，异化硝酸盐还原为氨（DNRA）细菌以及硝酸盐/亚硝酸盐依赖性厌氧甲烷氧化（NO _x-DAMO）微生物。在过去的十年中，高通量分子技术的发展使这些未成年人群体的检测，定量和表征成为可能。因此，本综述的目的是综合了解废水处理厂中这些“被忽视的” N循环微生物的分布，生态位和动力学特性的当前知识。还讨论了它们在新型废水脱氮工艺中的潜在应用。从微生物学，生态学和工程学角度全面了解这些被忽视的N循环微生物，将有助于设计和操作更有效，更可持续的生物脱氮工艺。