was the active and dominant methanotroph in Tibet lake sediments.

Methane (CH), an important greenhouse gas, significantly impacts the local and global climate. Our study focused on the composition and activity of methanotrophs residing in the lakes on the Tibetan Plateau, a hotspot for climate change research. Based on the field survey, the family had a much higher relative abundance in freshwater lakes than in brackish and saline lakes, accounting for ~92% of total aerobic methanotrophs. Using the microcosm sediment incubation with CH followed by high throughput sequencing and metagenomic analysis, we further demonstrated that the family was actively oxidizing CH. Moreover, various methylotrophs, such as the genera and , were detected in the C-labeled DNAs, which suggested their participation in CH-carbon sequential assimilation. The presence of CH metabolism, such as the tetrahydromethanopterin and the ribulose monophosphate pathways, was identified in the metagenome-assembled genomes of the family . Furthermore, they had the potential to adapt to oxygen-deficient conditions and utilize multiple electron acceptors, such as metal oxides (Fe), nitrate, and nitrite, for survival in the Tibet lakes. Our findings highlighted the predominance of and the associated microbes as active CH consumers, potentially regulating the CH emissions in the Tibet freshwater lakes. These insights contributed to understanding the plateau carbon cycle and emphasized the significance of methanotrophs in mitigating climate change.