Pyrimidine salvage pathways are essential to all cells. They provide a balance of RNA synthesis with the biosynthetic pathway in pyrimidine prototrophs and supply all the pyrimidine requirements in auxotrophs. While the pyrimidine biosynthetic pathway is found in almost all organisms and is nearly identical throughout nature, the salvage pathway often differs from species to species, with aspects of salvage seen in every organism. Thus significant taxonomic value may be ascribed to the salvage pathway. The pyrimidine salvage pathways were studied in 55 microorganisms. Nine different salvage motifs, grouped I-IX, were identified in this study based on the presence of different combinations of the following enzymes: cytidine deaminase (Cdd), cytosine deaminase (Cod), uridine phosphorylase (Udp), uracil phosphoribosyltransferase (Upp), uridine hydrolase (Udh), nucleoside hydrolase (Nuh), uridine/cytidine kinase (Udk), 5'-nucleotidase and CMP kinase (Cmk).