典型河口生态系统中全程硝化菌（Comammox）的时空分布、环境效应及其基因组比较研究

Nitrification plays a crucial role in maintaining the balance of global nitrogen cycling. The discovery of complete ammonia oxidizer (Comammox) has rewritten the 100-year-old dogma, and raising many important scientific questions in nitrification, such as the ecological distribution of these microorganisms in the environment and their contribution in the nitrogen cycle. In view of this, we choose the typical estuary-Pearl River Estuary as the study area, and the key functional gene amoA of these microorganisms as the marker gene, to investigate the abundance, expression and diversity of Comammox and their temporal and spatial variation by using quantitative PCR and high-throughput sequencing approaches. Meanwhile, we will also analyze the relationships between environmental factors and the Comammox amoA genes to assess their environmental effects. Secondly, the participation of Comammox in nitrification will be revealed by comparing with the abundance and expression of amoA genes of AOB, AOA and Comammox. Finally, Comammox from representative sediment samples will be enriched for genome reconstruction, thus the genome diversity and environmental adaption of Comammox will be analyzed. The results of this proposal will not only enhance the knowledge of Comammox, but also provide important scientific data for assessing their contribution in nitrification.

硝化作用在维持全球氮素平衡中起着至关重要的作用。全程硝化菌（Comammox）的发现终结了传承百年的经典两步硝化理论，并引出了大量与硝化作用相关的亟待解决的科学问题，如这类微生物在环境中的生态位及在氮循环中的贡献等。鉴于此，本项目拟以典型河口-珠江口为研究区域，以此类微生物的关键功能基因amoA为标志基因，采用定量PCR和高通量测序等技术，全面分析Comammox在珠江口淡水、淡咸水交接和咸水区三种典型水生沉积物环境中丰度、表达及多样性的时空变化规律，并结合环境参数，探讨其环境效应；其次，通过对比AOB和AOA amoA基因的丰度及表达，揭示Comammox在硝化作用中的参与度；最后，选取代表性站位的Comammox进行富集培养，通过宏基因组测序，揭示其基因组多样性及环境适应性。研究结果不仅可以丰富人们对Comammox的认识，也可为评估其在硝化作用的贡献提供重要的科学依据。

硝化作用在维持全球氮素平衡中起着至关重要的作用。全程硝化菌（Comammox）的发现是硝化作用研究的里程碑，它的发现改变了学术界对氨氧化微生物的认识，也为进一步揭示自然界氮循环及其微生物学过程打开了新的突破口。本项目以整个珠江口淡水、淡咸水交接和咸水区三种典型水生环境为研究区域，采用高通量测序和荧光定量PCR等技术对Comammox 的多样性、丰度、进化以及其环境因子驱动因素进行研究。研究结果显示，在珠江口区域，Comammox 呈现出丰富的多样性，以95%为阀值对amoA基因聚类，共获得了740个OTU。随着盐度的增加，其多样性显著降低。不同盐度区域的Comammox在进化上存在明显差异。定量PCR结果显示Comammox是淡水区硝化作用的主要参与者，而在中高盐度区域，Comammox的丰度显著低于氨氧化古菌（AOA）。通过中性群落模型、冗余分析以及相关性分析等，明确了Comammox从低盐度到高盐度区域的群落构建主要由确定过程(deterministic processes)主导，环境因子中，盐度，总氮以及铵盐对Comammox群落组成的影响最为显著。本研究扩展了人们对河口生态系统中Comammox多样性和生态位偏好的认识，并进一步加强了对Comammox从淡水到海洋环境群落构建过程的理解。