DNA and RNA sequencing reveal the role of rare bacterial taxa in constructed wetlands: Insights into community activities, ecological functions, and assembly processes

Microorganisms are essential for the functioning of constructed wetlands (CWs), yet the role of rare bacterial taxa in CWs remains poorly understood. In this study, the community structure, metabolic activities, ecological functions, and assembly processes of abundant and rare bacterial taxa in CWs were examined using DNA and RNA high-throughput sequencing. Our results revealed that Gammaproteobacteria, Alphaproteobacteria, Bacteroidia, and Actinobacteria exhibited high diversity and sequence abundance. Retention in CWs generally reduced the metabolic activities of bacterial communities, with intermediate and rare taxa showing significantly lower activity compared to those in the influent. Despite their low abundance, functional groups involved in nitrogen and phosphorus removal exhibited high metabolic activities, highlighting their crucial role in these processes. Co-occurrence network analysis showed that non-rare taxa interacted more frequently with rare taxa than with conspecifics, and that keystone species included comparable numbers of both abundant and rare species. These highlight the importance of rare taxa in ecological functions and maintaining the stability of bacterial community structure in CWs. The assembly of bacterial communities was driven by both deterministic and stochastic processes, with stochastic processes predominantly shaping the rare taxa and deterministic processes primarily influencing the abundant taxa. Overall, this study provides novel insights into bacterial community structure, metabolic activity, and assembly processes in CWs, particularly the ecological roles of rare taxa.