College of Engineering, Shibaura Institute of Technology, Tokyo, Japan.
Department of Applied Biosciences, Faculty of Life Sciences, Toyo University, Gunma, Japan.
Appl Microbiol Biotechnol. 2024 Oct 24;108(1):494. doi: 10.1007/s00253-024-13306-z.
Nitrification is a vital process in the biological removal of inorganic nitrogen compounds. In order to ensure the stability and effectiveness of this process, buffer solutions should be added to the system to maintain neutral to slightly alkaline conditions. With a focus on the newly discovered comammox Nitrospira, this research investigates the transition of the nitrifying community within a biofilm reactor under different acidic levels (initiated at pH 6 and gradually decreased to pH 5). During the 305-day continuous operation experiment, it was observed that responsible ammonia oxidizers transitioned from ammonia-oxidizing bacteria (AOB) during the initial stages (setup stage and early stage of pH 6) to comammox Nitrospira under pH 5.5 and pH 5. Further analysis using next-generation sequencing targeting both the 16S rRNA region and amoA region revealed a shift in the dominant cluster of both Nitrospirae and comammox Nitrospira under varying pH conditions. Our study identified a distinct cluster of comammox Nitrospira that is phylogenetically closed to sequences found in acidic environments, but exhibits dissimilarity from known comammox Nitrospira isolates and the majority of environmental sequences. This cluster was found to be prevalent in the acidic biofilm reactor studied and thrived particularly well at pH 5. These findings underscore the potential significance of this distinct, uncultivated group of comammox Nitrospira in performing ammonia oxidation under acidic conditions. KEY POINTS: • Ammonia was effectively removed under pH 5.5 and 5 in the biofilm reactor • The dominant ammonia oxidizer was comammox Nitrospira when pH was 5.5 and 5 • A potential acidophilic cluster of comammox Nitrospira was identified in this acidic biofilm reactor.
硝化作用是生物去除无机含氮化合物的重要过程。为了确保该过程的稳定性和有效性，应向系统中添加缓冲溶液，以维持中性至微碱性条件。本研究以新发现的共氨氧化菌（Comammox Nitrospira）为重点，研究了在不同酸度（起始 pH 值为 6，逐渐降至 5）下生物膜反应器中硝化菌群的转变。在 305 天的连续运行实验中，观察到在起始 pH 值为 6 的阶段（启动阶段和 pH 6 的早期阶段），负责氨氧化的氨氧化菌（AOB）转变为 pH 5.5 和 pH 5 下的共氨氧化菌（Comammox Nitrospira）。使用靶向 16S rRNA 区和 amoA 区的下一代测序进行的进一步分析表明，在不同 pH 条件下，Nitrospirae 和共氨氧化菌（Comammox Nitrospira）的优势菌群发生了转变。本研究鉴定出一个独特的共氨氧化菌（Comammox Nitrospira）聚类，该聚类在系统发育上与在酸性环境中发现的序列密切相关，但与已知的共氨氧化菌（Comammox Nitrospira）分离株和大多数环境序列不同。该聚类在研究的酸性生物膜反应器中普遍存在，在 pH 5 时特别旺盛。这些发现强调了这个独特的、未培养的共氨氧化菌（Comammox Nitrospira）在酸性条件下进行氨氧化的潜在重要性。
