MIMt-18S is composed of sequences from two different sources, sequences directly taken from the manually curated repository Targeted Loci from Refseq and sequences extracted from fully sequenced genomes deposited in Genbank and Refseq with the tool RNAmmer 1.2. For every genome, all 18S sequences were extracted and only kept in the database if they were not identical to another copy.

For the curated version (M2c), 18S sequences from Targeted Loci were joint to sequences extracted from Refseq genomes with RNAmmer software, and those sequences 100% redundant with another one present in the database was included in the redundancy file indicating the sequence code and all the species represented by that sequence.

The full version of the MIMt 18S database is composed by all sequences contained in the curated version plus sequences from genomes of new species available only at Genbank.

In total, MIMt-18S_M2c contains 37,359 sequences belonging to 4,878 different species.

Full version of MIMt-18S contains in total 233,241 sequences belonging to 13,458 species.