Stable microbial community promotes aerobic methanotrophy in a large river-reservoir system

Aerobic methanotrophy, mainly carried out by methane-oxidizing bacteria (MOB) in freshwater systems, plays a crucial role in reducing methane (CH₄) emissions and serves as an additional carbon source (methane-derived carbon) that supports the development of microbial food loops. However, how hydrological gradients and trophic states jointly regulate methane-derived carbon dynamics and microbial community stability in river-reservoir systems, and the interplay between these two aspects, has not been adequately explored. Here, we analyze bacterial and microeukaryotic organisms using 16S rRNA and 18S rRNA gene sequencing, respectively, in a river-reservoir complex in the upper Yangtze River basin. Our results show that species diversity and interaction strength with MOB are key to maintaining community stability in the riverine zone. In addition, the more pronounced niche differentiation also contributes to community stability in the lacustrine zone, which in turn facilitates the function of aerobic methanotrophy. In the riverine and lacustrine zones, the keystone species shift from the Alphaproteobacteria class (Alpha-MOB) to the Gammaproteobacteria class (Gamma-MOB), indicating distinct mechanisms for maintaining community stability in these zones. Moreover, methane-derived carbon in the riverine and lacustrine zones and in the mesotrophic states is crucial for supporting bacterial productivity and is associated with the highest community stability. These insights highlight the complex but important role of aerobic methanotrophy in freshwater systems.

Our study elucidates the ecological underpinnings of aerobic methanotrophy (methane-derived carbon) in freshwater systems, revealing a pivotal role of community stability in modulating aerobic methanotrophy across hydrological gradients. We identify a shift in dominant methane-oxidizing bacteria (MOB) classes from Alpha- to Gammaproteobacteria, highlighting distinct mechanisms for community stability maintenance and methane-derived carbon utilization, crucial for bacterial productivity and ecosystem health. This study enhances our understanding of methane dynamics in freshwater systems, a subject with significant implications for climate change mitigation, and provides valuable insights into the microbial food loop and carbon cycling, aligning with the focus of mSystems.