Metabolic Versatility of Prokaryotes for Urea Decomposition

In this issue of the Journal of Bacteriology, Kanamori et al. (6) present evidence that Oleomonas sagaranensis, an α-proteobacterium, metabolizes urea by two distinct pathways. On the one hand, this microorganism directly hydrolyzes urea by action of urease, an enzyme that is widely distributed in prokaryotes, fungi, and plants. In addition, O. sagaranensis decomposes urea by use of urea amidolyase, an activity heretofore observed only in selected yeast and green algae. Of more general interest, sequence database searches suggest that the latter pathway is present in numerous other prokaryotes; thus, this alternative pathway for urea decomposition may be more prevalent than generally appreciated. These results inspire questions about why a microbe would possess two routes for urea degradation, how the two pathways are regulated and utilized in the cell, and whether one pathway might function in a role other than urea degradation.