Note: This is version 4.1 of the mOTUs marker gene database. It directly relates version 4.1 of the mOTUs genome database. Changes: The clustering, the mOTUs, the MGCs and MGs are unchanged from 4.0 to 4.1 ~150k MAGs from extreme environments were added. Those MAGs were associated with existing mOTUs where possible or assigned to the no_mOTU group Access to the functional annotation of the 150K MAGs added to the motus genomes routine Updated GTDB taxonomy from R220 to R226 for all genomes in the mOTUs database Database for the marker gene-based OTU (mOTU) tool (v4). The mOTUs profiler is a computational tool that estimates relative abundance of known and unknown microbial community members using metagenomic shotgun sequencing data. Github directory of the tool: link In the current version, 124,295 species-level taxonomic units (mOTUs) were constructed using sequences of 10 single-copy marker genes recovered from mOTUs-db, a collection of 2.83 million metagenome-assembled genomes (MAGs) and 919 090 single-cell and isolate genomes. 30,256 mOTUs are represented by an isolate genome, whereas 94,039 mOTUs are represented by MAGs only. The source genome database is accessible at https://motus-db.org/.