基于16S rRNA基因高通量绝对定量解析黄河入海口淡水与海水水体细菌群落特征

Characterization of bacterial communities in freshwater and seawater of the Yellow River estuary by 16S rRNA gene high-throughput absolute abundance quantification

摘要:

【目的】 黄河入海口地处河流-陆地-海洋的交汇地带，是淡水水体与海水水体相互作用的混合区域，也是多样化和生产力较强的河口生态系统。本研究以黄河入海口为研究对象，探究其淡水与海水水体细菌群落特征。【方法】 采用高通量绝对定量技术，获得细菌群落绝对丰度信息，在此基础上比较分析2种水体细菌群落优势物种组成、α和β多样性、网络共现模式、构建机制及潜在功能，并探究优势物种与水体环境因子的相关性。【结果】 淡水水体细菌的绝对拷贝数为2.61×10⁶ copies/mL，是海水的1.8倍。2种水体共同优势菌门为放线菌门、假单胞菌门、蓝细菌门和拟杆菌门等，其各自绝对丰度有明显差异。淡水中放线菌门数量最高，约等于海水中所有优势菌门数量之和，而海水中假单胞菌门数量最高。淡水水体细菌群落α多样性高于海水，2种水体细菌群落结构存在较明显的差异，主要源于各自优势物种丰度的差异。淡水水体细菌共现网络较海水更复杂和稳定，随机性过程主导2种水体细菌群落构建机制。2种水体细菌群落功能结构存在差异，但拥有共性功能。新陈代谢是2种水体细菌群落丰度最高的功能，其在淡水中的相对丰度显著高于海水。5种环境因子[pH、氧化还原电位(oxidation-reduction potential, ORP)、电导率(electrical conductivity, EC)、总有机碳(total organic carbon, TOC)和总氮(total nitrogen, TN)]与水体优势物种分别具有不同程度的相关性。除EC外的4种环境因子间均存在共线性关系，与pH、TOC和TN呈正相关关系的优势菌属均与ORP呈负相关，反之亦然。放线菌门和假单胞菌门分别与pH呈正相关和负相关关系。【结论】 黄河入海口淡水和海水水体细菌群落特征存在较大差异，主要体现在细菌数量、多样性、功能结构和共现网络上，但2种水体具有相似的优势物种组成和群落构建机制。本研究结果可为黄河入海口水体微生物生态学研究及开发利用微生物资源提供数据支持。

Abstract:

[Objective] The Yellow River estuary located at the confluence of the Yellow River, land, and ocean is an area with mixed freshwater and seawater and a diverse and productive estuary ecosystem. This study aims to characterize the bacterial communities in freshwater and seawater of the Yellow River estuary. [Methods] High-throughput absolute abundance quantification was adopted to measure the absolute abundance of bacterial communities. The dominant taxa, α and β diversity, co-occurrence network, assembly mechanisms, and potential functions were compared between the bacterial communities in freshwater and seawater. The correlations between dominant taxa and environmental factors were explored. [Results] The absolute abundance of bacteria in freshwater was 2.61×10⁶ copies/mL, which was 1.8 times of that in seawater. The common dominant phyla in freshwater and seawater were Actinomycetota, Pseudomonadota, Cyanobacteriota, and Bacteroidota, with significant differences in absolute abundance. The abundance of Actinomycetota ranked first in freshwater, which was approximately equal to the sum of all dominant phyla in seawater. The abundance of Pseudomonadota was the highest in seawater. The alpha diversity of bacteria in freshwater was higher than that in seawater. There were significant differences in the bacterial community structure between freshwater and seawater, mainly due to the differences in the abundance of the dominant taxa. The bacterial co-occurrence network in freshwater was more complex and stable than that in seawater, and stochastic processes dominated the bacterial community assembly in both freshwater and seawater. The bacterial communities in freshwater and seawater presented different functions, while they shared some common functions. Metabolism was the most abundant function, with higher relative abundance in freshwater than in seawater. Five environmental factors ((pH, oxidation-reduction potential (ORP), electrical conductivity (EC), total organic carbon (TOC), and total nitrogen (TN)) correlated with the dominant bacterial taxa to different extent. There were collinear relationships among the four environmental factors except EC. The dominant genera showing positive correlations with pH, TOC and TN were all negatively correlated with ORP, and vice versa. Actinomycetota and Pseudomonadota were positively and negatively correlated with pH, respectively. [Conclusion] The bacterial communities showed great differences between freshwater and seawater in the Yellow River estuary. The differences were mainly reflected in the abundance, diversity, functional structure, and co-occurrence network. The bacterial communities in freshwater and seawater had similar dominant taxa and assembly mechanisms. The results provide data support for studying the microbial ecology and exploiting microbial resources in the Yellow River estuary.