Abstract:[Background] Wetlands harbobring a variety of methane-producing archaea emit ample methane. The uncultured methanogens, Rice Cluster II (RCII), exist widely in cold acidic peatlands, freshwater lake wetlands, minerotrophic fens, and northern peat moss. However, the distribution and metabolic pathways of RCII in the low-temperature saline-alkaline wetlands remain unknown. [Objective] To investigate the diversity and infer the methanogenic pathways and potential adaptation mechanisms of RCII in saline-alkaline Zhalong wetland. [Methods] High-throughput sequencing of the 16S rRNA genes in the top layer of soil was performed to reveal the composition of methanogenic archaea. We established the 16S rRNA gene clone library to analyze the phylogenetic clusters of RCII. We then conducted metagenomic analysis to infer the methanogenic pathways and the possible saline-alkaline adaption mechanisms of the RCII in Zhalong wetland.[Results] The uncultured RCII methanogens accounted for 13.280%±0.019% of the total methanogenic archaea in Zhalong wetland and were clustered into three phylogenetic groups. Two metagenome-assembled genomes of RCII possessed the complete suite of genes involved in methanogenesis via reduction of carbon dioxide. Furthermore, the two RCII genomes contained the genes associated with the transport and synthesis of trehalose. [Conclusion] Abundant uncultured RCII methanogens inhabit the saline-alkaline Zhalong wetland, and they can produce methane by reducing carbon dioxide and use the compatible solute trehalose to adapt to the saline-alkaline environment.
