DNA sequences are gathered from GenBank. The genomes of 22 prokaryotes are scanned for HTs, B.subtilis, E.coli and H.influenzae genomes being given a special attention to illustrate our approach. In particular, B.subtilis and E.coli provide valuable benchmark thanks to the set of previous works addressing that very issue (12, 14, 16, (34) (35) (36) (37) . Signatures of about 12 000 species are obtained from genomic sequences longer than 1.5 kb. Sequences derived from the same species are concatenated for accuracy purposes. Species from the three domains of life, archaea ($260 species), bacteria ($3950 species) and eukarya ($6750 species) as well as viruses ($1300 species), are represented for a total amount of 1.0 Gb.