不同营养程度湖泊中细菌群落组成及其分子生态网络特征

长江中下游地区是我国淡水湖泊的主要集中区，随着社会和经济的快速发展，该地区绝大部分湖泊正处于富营养状态.作为湖泊生态系统中的分解者和生产者，细菌群落在维持物质循环和能量流动中扮演着极为重要的角色，然而其组成及种间关系对富营养化过程的响应机制仍不明确.利用16S rDNA测序技术和分子生态网络技术探讨了长江中下游10个湖泊水体中细菌群落的组成、结构及其网络拓扑关系等特征.结果表明:①根据湖泊水体的富营养化指数，长江中下游地区的湖泊可分为中度富营养湖泊和重度富营养湖泊两种，并且这两种湖泊中细菌群落的α多样性均无显著性差异.②在这两种湖泊中细菌群落的优势类群基本一致，如在纲水平上均以Actinobacteria、Acidimicrobiia、Sphingobacteriia和Betaproteobacteria为主，在属水平上均以Hgcl_clade和CL500-29_marine-group为主.然而，与丰富种亚群落相反，稀有种亚群落在这两种湖泊中具有显著的区别.③中度富营养湖泊中细菌群落生态网络的节点和边的数量均小于重度富营养湖泊，并且前者网络具有更多的物种协作关系，其网络的中心性也显著大于后者.研究显示，湖泊富营养化的加剧使得水体中细菌群落的组成，尤其是稀有种亚群落发生了显著的演替，并且明显地削弱了细菌群落物种之间的协作关系. 

Characteristics of Bacterial Communities and Their Co-Occurrence Networks in Lake Ecosystem with Different Trophic States

The middle and lower reaches of the Yangtze River is mainly the centralized region of freshwater lakes, most of which are moderately and severely eutrophicated and with rapid social and economic development. As the decomposer and primary producer in water bodies, bacterial microbes play a pivotal role in material cycle and energy flow. However, their responses to eutrophication in terms of composition and interspecific interactions are still unclear. To fill this gap, we explored the composition, structure and topological features of the bacterial communities in 10 lakes of the middle and lower reaches of the Yangze River by the 16S rDNA and molecular ecological network technologies. The results showed that these targeted lakes were divided into two categories based on their trophic levels:moderate and severe eutrophication. Particularly, the α diversity of bacterial communities in these two trophic levels were comparable. Although the bacterial community composition was significantly different in moderate and severe eutrophic status, they had a high overlap in dominant sub-communities, which were dominated by Actinobacteria, Acidimicrobiia, Sphingobacteriia, and Betaproteobacteria at the class level, and by Hgcl_clade and CL500-29_marine_group at the genus level. Unlike the dominant sub-communities, the rare sub-communities were significantly different in these two trophic levels. Further, the size of the bacterial networks was larger in moderate than severe eutrophic lakes. There were also more cooperative interactions in moderate severe eutrophic lakes, as well as the betweenness. Our study suggested that the aggravation of eutrophication induced an ecological succession of the bacterial communities, particularly the rare sub-communities. And the eutrophication also impaired the cooperative interactions of the bacterial communities.