Biosynthesis of polyamines in eukaryotes, Archaea, and bacteria

As with all metabolic pathways, not only has polyamine biosynthesis been subject to divergent and convergent evolution and horizontal gene transfer, but many pathogenic and commensal organisms have abandoned the task altogether and instead obtain polyamines from the environment. Reflecting primary metabolism in general, polyamine biosynthesis is more diverse in Bacteria than it is in eukaryotes and Archaea. Each of the three physiologically relevant triamines, that is, spermidine, sym -homospermidine, and sym -norspermidine, can be synthesized by at least two distinct, evolutionarily independent pathways. Synthesis of tetraamines has evolved independently in Bacteria, Archaea, plants, yeasts, and animals. Because of the relative ease of genomic sequencing and the ever-increasing number of complete genome sequences available, it will now be easier to determine which polyamines are likely to be present in an organism by using genomic rather than chemical analysis. The following chapter is a guide to the biosynthetic diversity of polyamine formation and the evolutionary mechanisms generating that diversity.