Characterization of Treponema denticola pyrF encoding orotidine-5'-monophosphate decarboxylase

The Treponema denticola ATCC 35405 genome annotation contains most of the genes for de novo pyrimidine biosynthesis. To initiate characterization of pyrimidine synthesis in Treponema, we focused on TDE2110 (the putative pyrF, encoding orotidine-5'-monophosphate decarboxlyase). Unlike the parent strain, an isogenic pyrF mutant was resistant to 5-fluoroorotic acid. In complex medium, growth of the pyrF mutant was independent of added uracil, indicating activity of a uracil uptake/salvage pathway. Transcription of pyrF was greatly reduced in T. denticola grown in excess uracil, demonstrating that de novo pyrimidine synthesis is regulated and suggesting a feedback mechanism. Treponema denticola PyrF complemented uracil auxotrophy in an Escherichia coli pyrF mutant. This study provides biochemical confirmation of T. denticola genome predictions of de novo and salvage pyrimidine pathways and provides proof of concept that pyrF has potential as a selectable marker in T. denticola.