Summary
Thermoplasmata is a widely distributed and ecologically important archaeal class in the phylum Euryarchaeota. Because few cultures and genomes are available, uncharacterized Thermoplasmata metabolisms remain unexplored. In this study, we obtained four medium‐ to high‐quality archaeal metagenome‐assembled genomes (MAGs) from the filamentous fragments of black‐odorous aquatic sediments (Foshan, Guangdong, China). Based on their 16S rRNA gene and ribosomal protein phylogenies, the four MAGs belong to the previously unnamed Thermoplasmata UBA10834 clade. We propose that this clade (five reference genomes from the Genome Taxonomy Database (GTDB) and four MAGs from this study) be considered a new order,
Candidatus
Gimiplasmatales. Metabolic pathway reconstructions indicated that the
Ca
. Gimiplasmatales MAGs can biosynthesize isoprenoids and nucleotides
de novo
. Additionally, some taxa have genes for formaldehyde and acetate assimilation, and the Wood–Ljungdahl CO
2
‐fixation pathway, indicating a mixotrophic lifestyle. Sulfur reduction, hydrogen metabolism, and arsenic detoxification pathways were predicted, indicating sulfur‐, hydrogen‐, and arsenic‐transformation potentials. Comparative genomics indicated that the H
4
F Wood–Ljungdahl pathway of both
Ca
. Gimiplasmatales and Methanomassiliicoccales was likely obtained by the interdomain lateral gene transfer from the Firmicutes. Collectively, this study elucidates the taxonomic and potential metabolic diversity of the new order
Ca
. Gimiplasmatales and the evolution of this subgroup and its sister lineage Methanomassiliicoccales.