Department of Civil and Environmental Engineering, Northwestern University, Evanston, IL, 60208, United States.
College of Chemistry and Environmental Engineering, Shenzhen University, Shenzhen, 518060, PR China; Shenzhen Key Laboratory of Environmental Chemistry and Ecological Remediation, Shenzhen University, Shenzhen, 518060, PR China; Department of Civil Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong.
Water Res. 2019 May 15;155:275-287. doi: 10.1016/j.watres.2019.02.020. Epub 2019 Feb 20.
Denitrification is the stepwise microbial reduction of nitrate or nitrite (NO) to nitrogen gas via the obligate intermediates nitric oxide (NO) and nitrous oxide (NO). Substantial NO accumulation has been reported in denitrifying enhanced biological phosphorus removal (EBPR) bioreactors enriched in denitrifying polyphosphate accumulating organisms (DPAOs), but little is known about underlying mechanisms for NO generation, prevalence of complete versus truncated denitrification pathways, or the impact of NO feed on DPAO-enriched consortia. To address this knowledge gap, we employed genome-resolved metagenomics to investigate nitrogen transformation potential in a NO fed denitrifying EBPR bioreactor enriched in Candidatus Accumulibacter and prone to NO accumulation. Our analysis yielded 41 near-complete metagenome-assembled genomes (MAGs), including two co-occurring Accumulibacter strains affiliated with clades IA and IC (the first published genome from this clade) and 39 non-PAO flanking bacterial genomes. The dominant Accumulibacter clade IA encoded genes for complete denitrification, while the lower abundance Accumulibacter clade IC harbored all denitrification genes except for a canonical respiratory NO reductase. Analysis of the 39 non-PAO MAGs revealed a high prevalence of taxa harboring an incomplete denitrification pathway. Of the 27 MAGs harboring capacity for at least one step in the denitrification pathway, 10 were putative NO producers lacking NO reductase, 16 were putative NO reducers that lacked at least one upstream denitrification gene, and only one harbored a complete denitrification pathway. We also documented increasing abundance over the course of reactor operation of putative NO producers. Our results suggest that the unusually high levels of NO production observed in this Accumulibacter-enriched consortium are linked in part to the selection for non-PAO flanking microorganisms with truncated denitrification pathways.
反硝化作用是指通过必需的中间产物一氧化氮 (NO) 和氧化亚氮 (NO) 将硝酸盐或亚硝酸盐 (NO) 逐步还原为氮气。在富含反硝化聚磷菌 (DPAO) 的反硝化增强生物除磷 (EBPR) 生物反应器中，已经报道了大量的 NO 积累，但对于 NO 生成的潜在机制、完全与截断反硝化途径的流行程度，或 NO 进料对 DPAO 富集共生体的影响知之甚少。为了解决这一知识空白，我们采用基因组解析宏基因组学来研究富含 Candidatus Accumulibacter 且易于 NO 积累的 NO 进料反硝化 EBPR 生物反应器中的氮转化潜力。我们的分析产生了 41 个近乎完整的宏基因组组装基因组 (MAGs)，其中包括两个共同出现的 Accumulibacter 菌株，它们与 IA 和 IC 群 (该群的第一个发表的基因组) 相关，以及 39 个非-PAO 侧翼细菌基因组。占主导地位的 Accumulibacter IA 群编码了完整的反硝化基因，而丰度较低的 Accumulibacter IC 群则拥有除了典型的呼吸性 NO 还原酶之外的所有反硝化基因。对 39 个非-PAO MAGs 的分析表明，携带不完全反硝化途径的分类群的流行率很高。在至少有一个反硝化途径步骤的 27 个 MAGs 中，有 10 个是没有 NO 还原酶的潜在的 NO 产生菌，有 16 个是没有至少一个上游反硝化基因的潜在的 NO 还原菌，只有一个具有完整的反硝化途径。我们还记录了在反应器运行过程中潜在的 NO 产生菌的丰度增加。我们的结果表明，在富含 Accumulibacter 的共生体中观察到的异常高水平的 NO 生成部分与选择具有截断反硝化途径的非-PAO 侧翼微生物有关。
