Pseudomonas - Taxonomy

Taxonomy

The studies on the taxonomy of this complicated genus groped their way in the dark while following the classical procedures developed for the description and identification of the organisms involved in sanitary bacteriology during the first decades of the 20th century. This situation sharply changed with the proposal to introduce as the central criterion the similarities in the composition and sequences of macromolecular components of the ribosomal RNA. The new methodology clearly showed the genus Pseudomonas, as classically defined, consisted in fact of a conglomerate of genera that could clearly be separated into five so-called rRNA homology groups. Moreover, the taxonomic studies suggested an approach that might prove useful in taxonomic studies of all other prokaryotic groups. A few decades after the proposal of the new genus Pseudomonas by Migula in 1894, the accumulation of species names assigned to the genus reached alarming proportions. At present, the number of species in the current list has contracted more than 90%. In fact, this approximated reduction may be even more dramatic if one considers the present list contains many new names, i.e., relatively few names of the original list survived in the process. The new methodology and the inclusion of approaches based on the studies of conservative macromolecules other than rRNA components, constitutes an effective prescription that helped to reduce Pseudomonas nomenclatural hypertrophy to a manageable size.